Conform more of the codebase to strictNullChecks (#10350

* Conform more of the codebase to `strictNullChecks`

* Iterate

* Generics ftw

* Iterate

src/@types/common.ts

@@ -52,3 +52,5 @@ export type KeysStartingWith<Input extends object, Str extends string> = {
     // eslint-disable-next-line @typescript-eslint/no-unused-vars
     [P in keyof Input]: P extends `${Str}${infer _X}` ? P : never; // we don't use _X
 }[keyof Input];
+
+export type NonEmptyArray<T> = [T, ...T[]];

src/AddThreepid.ts

@@ -26,7 +26,11 @@ import { SSOAuthEntry } from "./components/views/auth/InteractiveAuthEntryCompon
 import InteractiveAuthDialog from "./components/views/dialogs/InteractiveAuthDialog";
 
 function getIdServerDomain(): string {
-    return MatrixClientPeg.get().idBaseUrl.split("://")[1];
+    const idBaseUrl = MatrixClientPeg.get().idBaseUrl;
+    if (!idBaseUrl) {
+        throw new Error("Identity server not set");
+    }
+    return idBaseUrl.split("://")[1];
 }
 
 export type Binding = {
@@ -190,6 +194,9 @@ export default class AddThreepid {
                 if (this.bind) {
                     const authClient = new IdentityAuthClient();
                     const identityAccessToken = await authClient.getAccessToken();
+                    if (!identityAccessToken) {
+                        throw new Error("No identity access token found");
+                    }
                     await MatrixClientPeg.get().bindThreePid({
                         sid: this.sessionId,
                         client_secret: this.clientSecret,
@@ -279,7 +286,9 @@ export default class AddThreepid {
      * with a "message" property which contains a human-readable message detailing why
      * the request failed.
      */
-    public async haveMsisdnToken(msisdnToken: string): Promise<any[] | undefined> {
+    public async haveMsisdnToken(
+        msisdnToken: string,
+    ): Promise<[success?: boolean, result?: IAuthData | Error | null] | undefined> {
         const authClient = new IdentityAuthClient();
         const supportsSeparateAddAndBind = await MatrixClientPeg.get().doesServerSupportSeparateAddAndBind();
 

src/accessibility/context_menu/ContextMenuButton.tsx

@@ -39,7 +39,7 @@ export const ContextMenuButton: React.FC<IProps> = ({
         <AccessibleButton
             {...props}
             onClick={onClick}
-            onContextMenu={onContextMenu || onClick}
+            onContextMenu={onContextMenu ?? onClick ?? undefined}
             title={label}
             aria-label={label}
             aria-haspopup={true}

src/accessibility/context_menu/ContextMenuTooltipButton.tsx

@@ -37,7 +37,7 @@ export const ContextMenuTooltipButton: React.FC<IProps> = ({
         <AccessibleTooltipButton
             {...props}
             onClick={onClick}
-            onContextMenu={onContextMenu || onClick}
+            onContextMenu={onContextMenu ?? onClick ?? undefined}
             aria-haspopup={true}
             aria-expanded={isExpanded}
             forceHide={isExpanded}

src/actions/RoomListActions.ts

@@ -26,7 +26,7 @@ import { _t } from "../languageHandler";
 import { AsyncActionPayload } from "../dispatcher/payloads";
 import RoomListStore from "../stores/room-list/RoomListStore";
 import { SortAlgorithm } from "../stores/room-list/algorithms/models";
-import { DefaultTagID } from "../stores/room-list/models";
+import { DefaultTagID, TagID } from "../stores/room-list/models";
 import ErrorDialog from "../components/views/dialogs/ErrorDialog";
 
 export default class RoomListActions {
@@ -49,10 +49,10 @@ export default class RoomListActions {
     public static tagRoom(
         matrixClient: MatrixClient,
         room: Room,
-        oldTag: string,
+        oldTag: TagID | null,
-        newTag: string,
+        newTag: TagID | null,
-        oldIndex: number | null,
+        oldIndex?: number,
-        newIndex: number | null,
+        newIndex?: number,
     ): AsyncActionPayload {
         let metaData: Parameters<MatrixClient["setRoomTag"]>[2] | null = null;
 

src/audio/PlaybackQueue.ts

@@ -106,7 +106,7 @@ export class PlaybackQueue {
             // Remove the now-useless clock for some space savings
             this.clockStates.delete(mxEvent.getId()!);
 
-            if (wasLastPlaying) {
+            if (wasLastPlaying && this.currentPlaybackId) {
                 this.recentFullPlays.add(this.currentPlaybackId);
                 const orderClone = arrayFastClone(this.playbackIdOrder);
                 const last = orderClone.pop();
@@ -188,8 +188,8 @@ export class PlaybackQueue {
                 if (order.length === 0 || order[order.length - 1] !== this.currentPlaybackId) {
                     const lastInstance = this.playbacks.get(this.currentPlaybackId);
                     if (
-                        lastInstance.currentState === PlaybackState.Playing ||
+                        lastInstance &&
-                        lastInstance.currentState === PlaybackState.Paused
+                        [PlaybackState.Playing, PlaybackState.Paused].includes(lastInstance.currentState)
                     ) {
                         order.push(this.currentPlaybackId);
                     }

src/boundThreepids.ts

@@ -35,6 +35,9 @@ export async function getThreepidsWithBindStatus(
         try {
             const authClient = new IdentityAuthClient();
             const identityAccessToken = await authClient.getAccessToken({ check: false });
+            if (!identityAccessToken) {
+                throw new Error("No identity access token found");
+            }
 
             // Restructure for lookup query
             const query = threepids.map(({ medium, address }): [string, string] => [medium, address]);

src/components/structures/AutoHideScrollbar.tsx

@@ -29,7 +29,7 @@ export type IProps<T extends keyof JSX.IntrinsicElements> = Omit<DynamicHtmlElem
     onWheel?: (event: WheelEvent) => void;
     style?: React.CSSProperties;
     tabIndex?: number;
-    wrappedRef?: (ref: HTMLDivElement) => void;
+    wrappedRef?: (ref: HTMLDivElement | null) => void;
     children: ReactNode;
 };
 

src/components/structures/FilePanel.tsx

@@ -99,7 +99,7 @@ class FilePanel extends React.Component<IProps, IState> {
 
         const timeline = this.state.timelineSet.getLiveTimeline();
         if (ev.getType() !== "m.room.message") return;
-        if (["m.file", "m.image", "m.video", "m.audio"].indexOf(ev.getContent().msgtype) == -1) {
+        if (!["m.file", "m.image", "m.video", "m.audio"].includes(ev.getContent().msgtype!)) {
             return;
         }
 
@@ -176,7 +176,7 @@ class FilePanel extends React.Component<IProps, IState> {
         // the event index to fulfill the pagination request. Asking the server
         // to paginate won't ever work since the server can't correctly filter
         // out events containing URLs
-        if (client.isRoomEncrypted(roomId) && eventIndex !== null) {
+        if (room && client.isRoomEncrypted(roomId) && eventIndex !== null) {
             return eventIndex.paginateTimelineWindow(room, timelineWindow, direction, limit);
         } else {
             return timelineWindow.paginate(direction, limit);

src/components/structures/GenericDropdownMenu.tsx

@@ -177,7 +177,8 @@ export function GenericDropdownMenu<T>({
             </>
         );
     }
-    const contextMenu = menuDisplayed ? (
+    const contextMenu =
+        menuDisplayed && button.current ? (
             <ContextMenu
                 onFinished={closeMenu}
                 chevronFace={ChevronFace.Top}

src/components/structures/IndicatorScrollbar.tsx

@@ -44,7 +44,7 @@ export default class IndicatorScrollbar<T extends keyof JSX.IntrinsicElements> e
 > {
     private autoHideScrollbar = createRef<AutoHideScrollbar<any>>();
     private scrollElement: HTMLDivElement;
-    private likelyTrackpadUser: boolean = null;
+    private likelyTrackpadUser: boolean | null = null;
     private checkAgainForTrackpad = 0; // ts in milliseconds to recheck this._likelyTrackpadUser
 
     public constructor(props: IProps<T>) {

src/components/structures/LeftPanel.tsx

@@ -271,6 +271,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         // add appropriate sticky classes to wrapper so it has
         // the necessary top/bottom padding to put the sticky header in
         const listWrapper = list.parentElement; // .mx_LeftPanel_roomListWrapper
+        if (!listWrapper) return;
         if (lastTopHeader) {
             listWrapper.classList.add("mx_LeftPanel_roomListWrapper_stickyTop");
         } else {

src/components/structures/LegacyCallEventGrouper.ts

@@ -85,23 +85,23 @@ export default class LegacyCallEventGrouper extends EventEmitter {
         );
     }
 
-    private get invite(): MatrixEvent {
+    private get invite(): MatrixEvent | undefined {
         return [...this.events].find((event) => event.getType() === EventType.CallInvite);
     }
 
-    private get hangup(): MatrixEvent {
+    private get hangup(): MatrixEvent | undefined {
         return [...this.events].find((event) => event.getType() === EventType.CallHangup);
     }
 
-    private get reject(): MatrixEvent {
+    private get reject(): MatrixEvent | undefined {
         return [...this.events].find((event) => event.getType() === EventType.CallReject);
     }
 
-    private get selectAnswer(): MatrixEvent {
+    private get selectAnswer(): MatrixEvent | undefined {
         return [...this.events].find((event) => event.getType() === EventType.CallSelectAnswer);
     }
 
-    public get isVoice(): boolean {
+    public get isVoice(): boolean | undefined {
         const invite = this.invite;
         if (!invite) return;
 
@@ -114,7 +114,7 @@ export default class LegacyCallEventGrouper extends EventEmitter {
         return this.call?.hangupReason ?? this.hangup?.getContent()?.reason ?? null;
     }
 
-    public get rejectParty(): string {
+    public get rejectParty(): string | undefined {
         return this.reject?.getSender();
     }
 

src/components/structures/LoggedInView.tsx

@@ -170,7 +170,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         monitorSyncedPushRules(this._matrixClient.getAccountData("m.push_rules"), this._matrixClient);
         this._matrixClient.on(ClientEvent.Sync, this.onSync);
         // Call `onSync` with the current state as well
-        this.onSync(this._matrixClient.getSyncState(), null, this._matrixClient.getSyncStateData());
+        this.onSync(this._matrixClient.getSyncState(), null, this._matrixClient.getSyncStateData() ?? undefined);
         this._matrixClient.on(RoomStateEvent.Events, this.onRoomStateEvents);
 
         this.layoutWatcherRef = SettingsStore.watchSetting("layout", null, this.onCompactLayoutChanged);
@@ -271,11 +271,11 @@ class LoggedInView extends React.Component<IProps, IState> {
     }
 
     private loadResizerPreferences(): void {
-        let lhsSize = parseInt(window.localStorage.getItem("mx_lhs_size"), 10);
+        let lhsSize = parseInt(window.localStorage.getItem("mx_lhs_size")!, 10);
         if (isNaN(lhsSize)) {
             lhsSize = 350;
         }
-        this.resizer.forHandleWithId("lp-resizer").resize(lhsSize);
+        this.resizer.forHandleWithId("lp-resizer")?.resize(lhsSize);
     }
 
     private onAccountData = (event: MatrixEvent): void => {
@@ -291,13 +291,13 @@ class LoggedInView extends React.Component<IProps, IState> {
         });
     };
 
-    private onSync = (syncState: SyncState, oldSyncState?: SyncState, data?: ISyncStateData): void => {
+    private onSync = (syncState: SyncState | null, oldSyncState: SyncState | null, data?: ISyncStateData): void => {
         const oldErrCode = (this.state.syncErrorData?.error as MatrixError)?.errcode;
         const newErrCode = (data?.error as MatrixError)?.errcode;
         if (syncState === oldSyncState && oldErrCode === newErrCode) return;
 
         this.setState({
-            syncErrorData: syncState === SyncState.Error ? data : null,
+            syncErrorData: syncState === SyncState.Error ? data : undefined,
         });
 
         if (oldSyncState === SyncState.Prepared && syncState === SyncState.Syncing) {
@@ -355,7 +355,7 @@ class LoggedInView extends React.Component<IProps, IState> {
             const pinnedEventIds = pinStateEvent.getContent().pinned.slice(0, MAX_PINNED_NOTICES_PER_ROOM);
             for (const eventId of pinnedEventIds) {
                 const timeline = await this._matrixClient.getEventTimeline(room.getUnfilteredTimelineSet(), eventId);
-                const event = timeline.getEvents().find((ev) => ev.getId() === eventId);
+                const event = timeline?.getEvents().find((ev) => ev.getId() === eventId);
                 if (event) events.push(event);
             }
         }
@@ -390,7 +390,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         if (inputableElement?.focus) {
             inputableElement.focus();
         } else {
-            const inThread = !!document.activeElement.closest(".mx_ThreadView");
+            const inThread = !!document.activeElement?.closest(".mx_ThreadView");
             // refocusing during a paste event will make the paste end up in the newly focused element,
             // so dispatch synchronously before paste happens
             dis.dispatch(
@@ -533,11 +533,11 @@ class LoggedInView extends React.Component<IProps, IState> {
                 });
                 break;
             case KeyBindingAction.PreviousVisitedRoomOrSpace:
-                PlatformPeg.get().navigateForwardBack(true);
+                PlatformPeg.get()?.navigateForwardBack(true);
                 handled = true;
                 break;
             case KeyBindingAction.NextVisitedRoomOrSpace:
-                PlatformPeg.get().navigateForwardBack(false);
+                PlatformPeg.get()?.navigateForwardBack(false);
                 handled = true;
                 break;
         }
@@ -555,7 +555,7 @@ class LoggedInView extends React.Component<IProps, IState> {
                     );
                     SettingsStore.setValue(
                         "showHiddenEventsInTimeline",
-                        undefined,
+                        null,
                         SettingLevel.DEVICE,
                         !hiddenEventVisibility,
                     );
@@ -567,7 +567,7 @@ class LoggedInView extends React.Component<IProps, IState> {
 
         if (
             !handled &&
-            PlatformPeg.get().overrideBrowserShortcuts() &&
+            PlatformPeg.get()?.overrideBrowserShortcuts() &&
             ev.code.startsWith("Digit") &&
             ev.code !== "Digit0" && // this is the shortcut for reset zoom, don't override it
             isOnlyCtrlOrCmdKeyEvent(ev)
@@ -599,7 +599,7 @@ class LoggedInView extends React.Component<IProps, IState> {
             // If the user is entering a printable character outside of an input field
             // redirect it to the composer for them.
             if (!isClickShortcut && isPrintable && !getInputableElement(ev.target as HTMLElement)) {
-                const inThread = !!document.activeElement.closest(".mx_ThreadView");
+                const inThread = !!document.activeElement?.closest(".mx_ThreadView");
                 // synchronous dispatch so we focus before key generates input
                 dis.dispatch(
                     {

src/components/structures/MatrixChat.tsx

@@ -187,9 +187,9 @@ interface IState {
     // The ID of the room we're viewing. This is either populated directly
     // in the case where we view a room by ID or by RoomView when it resolves
     // what ID an alias points at.
-    currentRoomId?: string;
+    currentRoomId: string | null;
     // If we're trying to just view a user ID (i.e. /user URL), this is it
-    currentUserId?: string;
+    currentUserId: string | null;
     // this is persisted as mx_lhs_size, loaded in LoggedInView
     collapseLhs: boolean;
     // Parameters used in the registration dance with the IS
@@ -202,7 +202,7 @@ interface IState {
     // When showing Modal dialogs we need to set aria-hidden on the root app element
     // and disable it when there are no dialogs
     hideToSRUsers: boolean;
-    syncError?: Error;
+    syncError: Error | null;
     resizeNotifier: ResizeNotifier;
     serverConfig?: ValidatedServerConfig;
     ready: boolean;
@@ -248,6 +248,8 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.state = {
             view: Views.LOADING,
             collapseLhs: false,
+            currentRoomId: null,
+            currentUserId: null,
 
             hideToSRUsers: false,
 
@@ -469,9 +471,9 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         );
     }, 1000);
 
-    private getFallbackHsUrl(): string {
+    private getFallbackHsUrl(): string | null {
         if (this.props.serverConfig?.isDefault) {
-            return this.props.config.fallback_hs_url;
+            return this.props.config.fallback_hs_url ?? null;
         } else {
             return null;
         }
@@ -480,7 +482,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     private getServerProperties(): { serverConfig: ValidatedServerConfig } {
         let props = this.state.serverConfig;
         if (!props) props = this.props.serverConfig; // for unit tests
-        if (!props) props = SdkConfig.get("validated_server_config");
+        if (!props) props = SdkConfig.get("validated_server_config")!;
         return { serverConfig: props };
     }
 
@@ -709,7 +711,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 Modal.createDialog(
                     UserSettingsDialog,
                     { initialTabId: tabPayload.initialTabId as UserTab },
-                    /*className=*/ null,
+                    /*className=*/ undefined,
                     /*isPriority=*/ false,
                     /*isStatic=*/ true,
                 );
@@ -978,7 +980,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.setState(
             {
                 view: Views.LOGGED_IN,
-                currentRoomId: roomInfo.room_id || null,
+                currentRoomId: roomInfo.room_id ?? null,
                 page_type: PageType.RoomView,
                 threepidInvite: roomInfo.threepid_invite,
                 roomOobData: roomInfo.oob_data,
@@ -1063,7 +1065,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
 
         const [shouldCreate, opts] = await modal.finished;
         if (shouldCreate) {
-            createRoom(opts);
+            createRoom(opts!);
         }
     }
 
@@ -1122,7 +1124,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         // Show a warning if there are additional complications.
         const warnings: JSX.Element[] = [];
 
-        const memberCount = roomToLeave.currentState.getJoinedMemberCount();
+        const memberCount = roomToLeave?.currentState.getJoinedMemberCount();
         if (memberCount === 1) {
             warnings.push(
                 <span className="warning" key="only_member_warning">
@@ -1137,7 +1139,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             return warnings;
         }
 
-        const joinRules = roomToLeave.currentState.getStateEvents("m.room.join_rules", "");
+        const joinRules = roomToLeave?.currentState.getStateEvents("m.room.join_rules", "");
         if (joinRules) {
             const rule = joinRules.getContent().join_rule;
             if (rule !== "public") {
@@ -1165,9 +1167,11 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 <span>
                     {isSpace
                         ? _t("Are you sure you want to leave the space '%(spaceName)s'?", {
-                              spaceName: roomToLeave.name,
+                              spaceName: roomToLeave?.name ?? _t("Unnamed Space"),
                           })
-                        : _t("Are you sure you want to leave the room '%(roomName)s'?", { roomName: roomToLeave.name })}
+                        : _t("Are you sure you want to leave the room '%(roomName)s'?", {
+                              roomName: roomToLeave?.name ?? _t("Unnamed Room"),
+                          })}
                     {warnings}
                 </span>
             ),
@@ -1311,9 +1315,9 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         this.setStateForNewView({ view: Views.LOGGED_IN });
         // If a specific screen is set to be shown after login, show that above
         // all else, as it probably means the user clicked on something already.
-        if (this.screenAfterLogin && this.screenAfterLogin.screen) {
+        if (this.screenAfterLogin?.screen) {
             this.showScreen(this.screenAfterLogin.screen, this.screenAfterLogin.params);
-            this.screenAfterLogin = null;
+            this.screenAfterLogin = undefined;
         } else if (MatrixClientPeg.currentUserIsJustRegistered()) {
             MatrixClientPeg.setJustRegisteredUserId(null);
 
@@ -1403,7 +1407,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         // result in view_home_page, _user_settings or _room_directory
         if (this.screenAfterLogin && this.screenAfterLogin.screen) {
             this.showScreen(this.screenAfterLogin.screen, this.screenAfterLogin.params);
-            this.screenAfterLogin = null;
+            this.screenAfterLogin = undefined;
         } else if (localStorage && localStorage.getItem("mx_last_room_id")) {
             // Before defaulting to directory, show the last viewed room
             this.viewLastRoom();
@@ -1419,7 +1423,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     private viewLastRoom(): void {
         dis.dispatch<ViewRoomPayload>({
             action: Action.ViewRoom,
-            room_id: localStorage.getItem("mx_last_room_id"),
+            room_id: localStorage.getItem("mx_last_room_id") ?? undefined,
             metricsTrigger: undefined, // other
         });
     }
@@ -1486,12 +1490,12 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             return this.loggedInView.current.canResetTimelineInRoom(roomId);
         });
 
-        cli.on(ClientEvent.Sync, (state: SyncState, prevState?: SyncState, data?: ISyncStateData) => {
+        cli.on(ClientEvent.Sync, (state: SyncState, prevState: SyncState | null, data?: ISyncStateData) => {
             if (state === SyncState.Error || state === SyncState.Reconnecting) {
-                if (data.error instanceof InvalidStoreError) {
+                if (data?.error instanceof InvalidStoreError) {
                     Lifecycle.handleInvalidStoreError(data.error);
                 }
-                this.setState({ syncError: data.error });
+                this.setState({ syncError: data?.error ?? null });
             } else if (this.state.syncError) {
                 this.setState({ syncError: null });
             }
@@ -1559,12 +1563,12 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                     cancelButton: _t("Dismiss"),
                     onFinished: (confirmed) => {
                         if (confirmed) {
-                            const wnd = window.open(consentUri, "_blank");
+                            const wnd = window.open(consentUri, "_blank")!;
                             wnd.opener = null;
                         }
                     },
                 },
-                null,
+                undefined,
                 true,
             );
         });
@@ -1655,7 +1659,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                     {
                         verifier: request.verifier,
                     },
-                    null,
+                    undefined,
                     /* priority = */ false,
                     /* static = */ true,
                 );
@@ -1774,7 +1778,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             }
 
             const type = screen === "start_sso" ? "sso" : "cas";
-            PlatformPeg.get().startSingleSignOn(cli, type, this.getFragmentAfterLogin());
+            PlatformPeg.get()?.startSingleSignOn(cli, type, this.getFragmentAfterLogin());
         } else if (screen.indexOf("room/") === 0) {
             // Rooms can have the following formats:
             // #room_alias:domain or !opaque_id:domain
@@ -1786,7 +1790,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 eventOffset = domainOffset + room.substring(domainOffset).indexOf("/");
             }
             const roomString = room.substring(0, eventOffset);
-            let eventId = room.substring(eventOffset + 1); // empty string if no event id given
+            let eventId: string | undefined = room.substring(eventOffset + 1); // empty string if no event id given
 
             // Previously we pulled the eventID from the segments in such a way
             // where if there was no eventId then we'd get undefined. However, we
@@ -1797,9 +1801,9 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
 
             // TODO: Handle encoded room/event IDs: https://github.com/vector-im/element-web/issues/9149
 
-            let threepidInvite: IThreepidInvite;
+            let threepidInvite: IThreepidInvite | undefined;
             // if we landed here from a 3PID invite, persist it
-            if (params.signurl && params.email) {
+            if (params?.signurl && params?.email) {
                 threepidInvite = ThreepidInviteStore.instance.storeInvite(
                     roomString,
                     params as IThreepidInviteWireFormat,
@@ -1816,8 +1820,8 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             // to other levels. If there's just one ?via= then params.via is a
             // single string. If someone does something like ?via=one.com&via=two.com
             // then params.via is an array of strings.
-            let via = [];
+            let via: string[] = [];
-            if (params.via) {
+            if (params?.via) {
                 if (typeof params.via === "string") via = [params.via];
                 else via = params.via;
             }
@@ -1855,7 +1859,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             dis.dispatch({
                 action: "view_user_info",
                 userId: userId,
-                subAction: params.action,
+                subAction: params?.action,
             });
         } else {
             logger.info("Ignoring showScreen for '%s'", screen);
@@ -1949,8 +1953,8 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         const numUnreadRooms = notificationState.numUnreadStates; // we know that states === rooms here
 
         if (PlatformPeg.get()) {
-            PlatformPeg.get().setErrorStatus(state === SyncState.Error);
+            PlatformPeg.get()!.setErrorStatus(state === SyncState.Error);
-            PlatformPeg.get().setNotificationCount(numUnreadRooms);
+            PlatformPeg.get()!.setNotificationCount(numUnreadRooms);
         }
 
         this.subTitleStatus = "";
@@ -1971,7 +1975,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     };
 
     private makeRegistrationUrl = (params: QueryDict): string => {
-        if (this.props.startingFragmentQueryParams.referrer) {
+        if (this.props.startingFragmentQueryParams?.referrer) {
             params.referrer = this.props.startingFragmentQueryParams.referrer;
         }
         return this.props.makeRegistrationUrl(params);

src/components/structures/MessagePanel.tsx

@@ -163,7 +163,7 @@ interface IProps {
     stickyBottom?: boolean;
 
     // className for the panel
-    className: string;
+    className?: string;
 
     // show twelve hour timestamps
     isTwelveHour?: boolean;
@@ -177,7 +177,7 @@ interface IProps {
     // which layout to use
     layout?: Layout;
 
-    resizeNotifier: ResizeNotifier;
+    resizeNotifier?: ResizeNotifier;
     permalinkCreator?: RoomPermalinkCreator;
     editState?: EditorStateTransfer;
 
@@ -345,12 +345,12 @@ export default class MessagePanel extends React.Component<IProps, IState> {
     };
 
     /* get the DOM node representing the given event */
-    public getNodeForEventId(eventId: string): HTMLElement {
+    public getNodeForEventId(eventId: string): HTMLElement | undefined {
         if (!this.eventTiles) {
             return undefined;
         }
 
-        return this.eventTiles[eventId]?.ref?.current;
+        return this.eventTiles[eventId]?.ref?.current ?? undefined;
     }
 
     public getTileForEventId(eventId?: string): UnwrappedEventTile | undefined {
@@ -362,7 +362,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
 
     /* return true if the content is fully scrolled down right now; else false.
      */
-    public isAtBottom(): boolean {
+    public isAtBottom(): boolean | undefined {
         return this.scrollPanel.current?.isAtBottom();
     }
 
@@ -371,7 +371,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
      *
      * returns null if we are not mounted.
      */
-    public getScrollState(): IScrollState {
+    public getScrollState(): IScrollState | null {
         return this.scrollPanel.current?.getScrollState() ?? null;
     }
 
@@ -381,7 +381,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
     //  -1: read marker is above the window
     //   0: read marker is within the window
     //  +1: read marker is below the window
-    public getReadMarkerPosition(): number {
+    public getReadMarkerPosition(): number | null {
         const readMarker = this.readMarkerNode.current;
         const messageWrapper = this.scrollPanel.current;
 
@@ -633,9 +633,8 @@ export default class MessagePanel extends React.Component<IProps, IState> {
             break;
         }
 
-        const ret = [];
+        const ret: ReactNode[] = [];
-
+        let prevEvent: MatrixEvent | null = null; // the last event we showed
-        let prevEvent = null; // the last event we showed
 
         // Note: the EventTile might still render a "sent/sending receipt" independent of
         // this information. When not providing read receipt information, the tile is likely
@@ -645,7 +644,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
             this.readReceiptsByEvent = this.getReadReceiptsByShownEvent();
         }
 
-        let grouper: BaseGrouper = null;
+        let grouper: BaseGrouper | null = null;
 
         for (let i = 0; i < events.length; i++) {
             const { event: mxEv, shouldShow } = events[i];
@@ -695,14 +694,14 @@ export default class MessagePanel extends React.Component<IProps, IState> {
     }
 
     public getTilesForEvent(
-        prevEvent: MatrixEvent,
+        prevEvent: MatrixEvent | null,
         mxEv: MatrixEvent,
         last = false,
         isGrouped = false,
         nextEvent?: MatrixEvent,
         nextEventWithTile?: MatrixEvent,
     ): ReactNode[] {
-        const ret = [];
+        const ret: ReactNode[] = [];
 
         const isEditing = this.props.editState?.getEvent().getId() === mxEv.getId();
         // local echoes have a fake date, which could even be yesterday. Treat them as 'today' for the date separators.
@@ -806,7 +805,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
         return ret;
     }
 
-    public wantsDateSeparator(prevEvent: MatrixEvent, nextEventDate: Date): boolean {
+    public wantsDateSeparator(prevEvent: MatrixEvent | null, nextEventDate: Date): boolean {
         if (this.context.timelineRenderingType === TimelineRenderingType.ThreadsList) {
             return false;
         }
@@ -820,7 +819,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
 
     // Get a list of read receipts that should be shown next to this event
     // Receipts are objects which have a 'userId', 'roomMember' and 'ts'.
-    private getReadReceiptsForEvent(event: MatrixEvent): IReadReceiptProps[] {
+    private getReadReceiptsForEvent(event: MatrixEvent): IReadReceiptProps[] | null {
         const myUserId = MatrixClientPeg.get().credentials.userId;
 
         // get list of read receipts, sorted most recent first
@@ -939,7 +938,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
     private onTypingShown = (): void => {
         const scrollPanel = this.scrollPanel.current;
         // this will make the timeline grow, so checkScroll
-        scrollPanel.checkScroll();
+        scrollPanel?.checkScroll();
         if (scrollPanel && scrollPanel.getScrollState().stuckAtBottom) {
             scrollPanel.preventShrinking();
         }
@@ -1018,7 +1017,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
             );
         }
 
-        let ircResizer = null;
+        let ircResizer: JSX.Element | undefined;
         if (this.props.layout == Layout.IRC) {
             ircResizer = (
                 <IRCTimelineProfileResizer
@@ -1076,7 +1075,7 @@ abstract class BaseGrouper {
     public constructor(
         public readonly panel: MessagePanel,
         public readonly event: MatrixEvent,
-        public readonly prevEvent: MatrixEvent,
+        public readonly prevEvent: MatrixEvent | null,
         public readonly lastShownEvent: MatrixEvent,
         public readonly nextEvent?: MatrixEvent,
         public readonly nextEventTile?: MatrixEvent,
@@ -1261,7 +1260,7 @@ class MainGrouper extends BaseGrouper {
     public constructor(
         public readonly panel: MessagePanel,
         public readonly event: MatrixEvent,
-        public readonly prevEvent: MatrixEvent,
+        public readonly prevEvent: MatrixEvent | null,
         public readonly lastShownEvent: MatrixEvent,
         nextEvent: MatrixEvent,
         nextEventTile: MatrixEvent,
@@ -1341,7 +1340,7 @@ class MainGrouper extends BaseGrouper {
         }
 
         let highlightInSummary = false;
-        let eventTiles = this.events
+        let eventTiles: ReactNode[] | null = this.events
             .map((e, i) => {
                 if (e.getId() === panel.props.highlightedEventId) {
                     highlightInSummary = true;

src/components/structures/ScrollPanel.tsx

@@ -149,7 +149,7 @@ interface IProps {
  */
 
 export interface IScrollState {
-    stuckAtBottom: boolean;
+    stuckAtBottom?: boolean;
     trackedNode?: HTMLElement;
     trackedScrollToken?: string;
     bottomOffset?: number;
@@ -173,7 +173,7 @@ export default class ScrollPanel extends React.Component<IProps> {
         onScroll: function () {},
     };
 
-    private readonly pendingFillRequests: Record<"b" | "f", boolean> = {
+    private readonly pendingFillRequests: Record<"b" | "f", boolean | null> = {
         b: null,
         f: null,
     };
@@ -190,7 +190,7 @@ export default class ScrollPanel extends React.Component<IProps> {
     private pendingFillDueToPropsUpdate: boolean;
     private scrollState: IScrollState;
     private preventShrinkingState: IPreventShrinkingState;
-    private unfillDebouncer: number;
+    private unfillDebouncer: number | null;
     private bottomGrowth: number;
     private minListHeight: number;
     private heightUpdateInProgress: boolean;

src/components/structures/TabbedView.tsx

@@ -24,6 +24,7 @@ import { _t } from "../../languageHandler";
 import AutoHideScrollbar from "./AutoHideScrollbar";
 import AccessibleButton from "../views/elements/AccessibleButton";
 import { PosthogScreenTracker, ScreenName } from "../../PosthogTrackers";
+import { NonEmptyArray } from "../../@types/common";
 
 /**
  * Represents a tab for the TabbedView.
@@ -40,7 +41,7 @@ export class Tab {
     public constructor(
         public readonly id: string,
         public readonly label: string,
-        public readonly icon: string,
+        public readonly icon: string | null,
         public readonly body: React.ReactNode,
         public readonly screenName?: ScreenName,
     ) {}
@@ -52,7 +53,7 @@ export enum TabLocation {
 }
 
 interface IProps {
-    tabs: Tab[];
+    tabs: NonEmptyArray<Tab>;
     initialTabId?: string;
     tabLocation: TabLocation;
     onChange?: (tabId: string) => void;
@@ -69,7 +70,7 @@ export default class TabbedView extends React.Component<IProps, IState> {
 
         const initialTabIdIsValid = props.tabs.find((tab) => tab.id === props.initialTabId);
         this.state = {
-            activeTabId: initialTabIdIsValid ? props.initialTabId : props.tabs[0]?.id,
+            activeTabId: initialTabIdIsValid ? props.initialTabId! : props.tabs[0].id,
         };
     }
 
@@ -101,7 +102,7 @@ export default class TabbedView extends React.Component<IProps, IState> {
 
         if (this.state.activeTabId === tab.id) classes += "mx_TabbedView_tabLabel_active";
 
-        let tabIcon = null;
+        let tabIcon: JSX.Element | undefined;
         if (tab.icon) {
             tabIcon = <span className={`mx_TabbedView_maskedIcon ${tab.icon}`} />;
         }
@@ -141,9 +142,11 @@ export default class TabbedView extends React.Component<IProps, IState> {
             mx_TabbedView_tabsOnTop: this.props.tabLocation == TabLocation.TOP,
         });
 
+        const screenName = tab?.screenName ?? this.props.screenName;
+
         return (
             <div className={tabbedViewClasses}>
-                <PosthogScreenTracker screenName={tab?.screenName ?? this.props.screenName} />
+                {screenName && <PosthogScreenTracker screenName={screenName} />}
                 <div className="mx_TabbedView_tabLabels">{labels}</div>
                 {panel}
             </div>

src/components/structures/TimelinePanel.tsx

@@ -200,7 +200,7 @@ interface IState {
     forwardPaginating: boolean;
 
     // cache of matrixClient.getSyncState() (but from the 'sync' event)
-    clientSyncState: SyncState;
+    clientSyncState: SyncState | null;
 
     // should the event tiles have twelve hour times
     isTwelveHour: boolean;
@@ -268,7 +268,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         // but for now we just do it per room for simplicity.
         let initialReadMarker: string | null = null;
         if (this.props.manageReadMarkers) {
-            const readmarker = this.props.timelineSet.room.getAccountData("m.fully_read");
+            const readmarker = this.props.timelineSet.room?.getAccountData("m.fully_read");
             if (readmarker) {
                 initialReadMarker = readmarker.getContent().event_id;
             } else {
@@ -414,7 +414,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         // Get the list of actually rendered events seen in the DOM.
         // This is useful to know for sure what's being shown on screen.
         // And we can suss out any corrupted React `key` problems.
-        let renderedEventIds: string[];
+        let renderedEventIds: string[] | undefined;
         try {
             const messagePanel = this.messagePanel.current;
             if (messagePanel) {
@@ -422,7 +422,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
                 if (messagePanelNode) {
                     const actuallyRenderedEvents = messagePanelNode.querySelectorAll("[data-event-id]");
                     renderedEventIds = [...actuallyRenderedEvents].map((renderedEvent) => {
-                        return renderedEvent.getAttribute("data-event-id");
+                        return renderedEvent.getAttribute("data-event-id")!;
                     });
                 }
             }
@@ -432,8 +432,8 @@ class TimelinePanel extends React.Component<IProps, IState> {
 
         // Get the list of events and threads for the room as seen by the
         // matrix-js-sdk.
-        let serializedEventIdsFromTimelineSets: { [key: string]: string[] }[];
+        let serializedEventIdsFromTimelineSets: { [key: string]: string[] }[] | undefined;
-        let serializedEventIdsFromThreadsTimelineSets: { [key: string]: string[] }[];
+        let serializedEventIdsFromThreadsTimelineSets: { [key: string]: string[] }[] | undefined;
         const serializedThreadsMap: { [key: string]: any } = {};
         if (room) {
             const timelineSets = room.getTimelineSets();
@@ -469,15 +469,15 @@ class TimelinePanel extends React.Component<IProps, IState> {
             }
         }
 
-        let timelineWindowEventIds: string[];
+        let timelineWindowEventIds: string[] | undefined;
         try {
-            timelineWindowEventIds = this.timelineWindow.getEvents().map((ev) => ev.getId());
+            timelineWindowEventIds = this.timelineWindow?.getEvents().map((ev) => ev.getId()!);
         } catch (err) {
             logger.error(`onDumpDebugLogs: Failed to get event IDs from the timelineWindow`, err);
         }
-        let pendingEventIds: string[];
+        let pendingEventIds: string[] | undefined;
         try {
-            pendingEventIds = this.props.timelineSet.getPendingEvents().map((ev) => ev.getId());
+            pendingEventIds = this.props.timelineSet.getPendingEvents().map((ev) => ev.getId()!);
         } catch (err) {
             logger.error(`onDumpDebugLogs: Failed to get pending event IDs`, err);
         }
@@ -491,10 +491,10 @@ class TimelinePanel extends React.Component<IProps, IState> {
                 `\tserializedEventIdsFromThreadsTimelineSets=` +
                 `${JSON.stringify(serializedEventIdsFromThreadsTimelineSets)}\n` +
                 `\tserializedThreadsMap=${JSON.stringify(serializedThreadsMap)}\n` +
-                `\ttimelineWindowEventIds(${timelineWindowEventIds.length})=${JSON.stringify(
+                `\ttimelineWindowEventIds(${timelineWindowEventIds?.length})=${JSON.stringify(
                     timelineWindowEventIds,
                 )}\n` +
-                `\tpendingEventIds(${pendingEventIds.length})=${JSON.stringify(pendingEventIds)}`,
+                `\tpendingEventIds(${pendingEventIds?.length})=${JSON.stringify(pendingEventIds)}`,
         );
     };
 
@@ -560,7 +560,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             return Promise.resolve(false);
         }
 
-        if (!this.timelineWindow.canPaginate(dir)) {
+        if (!this.timelineWindow?.canPaginate(dir)) {
             debuglog("can't", dir, "paginate any further");
             this.setState<null>({ [canPaginateKey]: false });
             return Promise.resolve(false);
@@ -576,7 +576,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
 
         return this.onPaginationRequest(this.timelineWindow, dir, PAGINATE_SIZE).then((r) => {
             if (this.unmounted) {
-                return;
+                return false;
             }
 
             debuglog("paginate complete backwards:" + backwards + "; success:" + r);
@@ -595,7 +595,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             // paginate in the other where we previously could not.
             const otherDirection = backwards ? EventTimeline.FORWARDS : EventTimeline.BACKWARDS;
             const canPaginateOtherWayKey = backwards ? "canForwardPaginate" : "canBackPaginate";
-            if (!this.state[canPaginateOtherWayKey] && this.timelineWindow.canPaginate(otherDirection)) {
+            if (!this.state[canPaginateOtherWayKey] && this.timelineWindow?.canPaginate(otherDirection)) {
                 debuglog("can now", otherDirection, "paginate again");
                 newState[canPaginateOtherWayKey] = true;
             }
@@ -666,7 +666,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
 
     private onRoomTimeline = (
         ev: MatrixEvent,
-        room: Room | null,
+        room: Room | undefined,
         toStartOfTimeline: boolean,
         removed: boolean,
         data: IRoomTimelineData,
@@ -1008,7 +1008,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         if (
             currentRREventId &&
             currentRREventIndex === null &&
-            this.timelineWindow.canPaginate(EventTimeline.FORWARDS)
+            this.timelineWindow?.canPaginate(EventTimeline.FORWARDS)
         ) {
             shouldSendRR = false;
         }
@@ -1149,7 +1149,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         const events = this.timelineWindow.getEvents();
 
         // first find where the current RM is
-        let i;
+        let i: number;
         for (i = 0; i < events.length; i++) {
             if (events[i].getId() == this.state.readMarkerEventId) {
                 break;
@@ -1182,7 +1182,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         //
         // Otherwise, reload the timeline rather than trying to paginate
         // through all of space-time.
-        if (this.timelineWindow.canPaginate(EventTimeline.FORWARDS)) {
+        if (this.timelineWindow?.canPaginate(EventTimeline.FORWARDS)) {
             this.loadTimeline();
         } else {
             this.messagePanel.current?.scrollToBottom();
@@ -1231,7 +1231,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
 
         // Look up the timestamp if we can find it
         const tl = this.props.timelineSet.getTimelineForEvent(rmId ?? "");
-        let rmTs: number;
+        let rmTs: number | undefined;
         if (tl) {
             const event = tl.getEvents().find((e) => {
                 return e.getId() == rmId;
@@ -1264,7 +1264,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
      *
      * returns null if we are not mounted.
      */
-    public getScrollState = (): IScrollState => {
+    public getScrollState = (): IScrollState | null => {
         if (!this.messagePanel.current) {
             return null;
         }
@@ -1277,7 +1277,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
     //  -1: read marker is above the window
     //   0: read marker is visible
     //  +1: read marker is below the window
-    public getReadMarkerPosition = (): number => {
+    public getReadMarkerPosition = (): number | null => {
         if (!this.props.manageReadMarkers) return null;
         if (!this.messagePanel.current) return null;
 
@@ -1449,7 +1449,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             this.setState({ timelineLoading: false });
             logger.error(`Error loading timeline panel at ${this.props.timelineSet.room?.roomId}/${eventId}`, error);
 
-            let onFinished: () => void;
+            let onFinished: (() => void) | undefined;
 
             // if we were given an event ID, then when the user closes the
             // dialog, let's jump to the end of the timeline. If we weren't,
@@ -1745,7 +1745,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         const wrapperRect = messagePanelNode.getBoundingClientRect();
         const myUserId = MatrixClientPeg.get().credentials.userId;
 
-        const isNodeInView = (node: HTMLElement): boolean => {
+        const isNodeInView = (node?: HTMLElement): boolean => {
             if (node) {
                 const boundingRect = node.getBoundingClientRect();
                 if (
@@ -1828,7 +1828,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             return null;
         }
 
-        const myUserId = client.credentials.userId;
+        const myUserId = client.getSafeUserId();
         const receiptStore: ReadReceipt<any, any> = this.props.timelineSet.thread ?? this.props.timelineSet.room;
         return receiptStore?.getEventReadUpTo(myUserId, ignoreSynthesized);
     }
@@ -1943,7 +1943,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
                 canBackPaginate={this.state.canBackPaginate && this.state.firstVisibleEventIndex === 0}
                 showUrlPreview={this.props.showUrlPreview}
                 showReadReceipts={this.props.showReadReceipts}
-                ourUserId={MatrixClientPeg.get().credentials.userId}
+                ourUserId={MatrixClientPeg.get().getSafeUserId()}
                 stickyBottom={stickyBottom}
                 onScroll={this.onMessageListScroll}
                 onFillRequest={this.onMessageListFillRequest}

src/components/structures/UserMenu.tsx

@@ -145,7 +145,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         } else {
             const theme = SettingsStore.getValue("theme");
             if (theme.startsWith("custom-")) {
-                return getCustomTheme(theme.substring("custom-".length)).is_dark;
+                return !!getCustomTheme(theme.substring("custom-".length)).is_dark;
             }
             return theme === "dark";
         }
@@ -236,7 +236,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         SettingsStore.setValue("theme", null, SettingLevel.DEVICE, newTheme); // set at same level as Appearance tab
     };
 
-    private onSettingsOpen = (ev: ButtonEvent, tabId: string): void => {
+    private onSettingsOpen = (ev: ButtonEvent, tabId?: string): void => {
         ev.preventDefault();
         ev.stopPropagation();
 
@@ -319,7 +319,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
             );
         }
 
-        let homeButton = null;
+        let homeButton: JSX.Element | undefined;
         if (this.hasHomePage) {
             homeButton = (
                 <IconizedContextMenuOption
@@ -330,7 +330,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
             );
         }
 
-        let feedbackButton;
+        let feedbackButton: JSX.Element | undefined;
         if (SettingsStore.getValue(UIFeature.Feedback)) {
             feedbackButton = (
                 <IconizedContextMenuOption
@@ -357,7 +357,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
                 <IconizedContextMenuOption
                     iconClassName="mx_UserMenu_iconSettings"
                     label={_t("All settings")}
-                    onClick={(e) => this.onSettingsOpen(e, null)}
+                    onClick={(e) => this.onSettingsOpen(e)}
                 />
                 {feedbackButton}
                 <IconizedContextMenuOption
@@ -376,7 +376,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
                     <IconizedContextMenuOption
                         iconClassName="mx_UserMenu_iconSettings"
                         label={_t("Settings")}
-                        onClick={(e) => this.onSettingsOpen(e, null)}
+                        onClick={(e) => this.onSettingsOpen(e)}
                     />
                     {feedbackButton}
                 </IconizedContextMenuOptionList>
@@ -395,9 +395,12 @@ export default class UserMenu extends React.Component<IProps, IState> {
                             {OwnProfileStore.instance.displayName}
                         </span>
                         <span className="mx_UserMenu_contextMenu_userId">
-                            {UserIdentifierCustomisations.getDisplayUserIdentifier(MatrixClientPeg.get().getUserId(), {
+                            {UserIdentifierCustomisations.getDisplayUserIdentifier(
+                                MatrixClientPeg.get().getSafeUserId(),
+                                {
                                     withDisplayName: true,
-                            })}
+                                },
+                            )}
                         </span>
                     </div>
 
@@ -426,7 +429,7 @@ export default class UserMenu extends React.Component<IProps, IState> {
         const displayName = OwnProfileStore.instance.displayName || userId;
         const avatarUrl = OwnProfileStore.instance.getHttpAvatarUrl(avatarSize);
 
-        let name: JSX.Element;
+        let name: JSX.Element | undefined;
         if (!this.props.isPanelCollapsed) {
             name = <div className="mx_UserMenu_name">{displayName}</div>;
         }

src/components/structures/ViewSource.tsx

@@ -68,7 +68,7 @@ export default class ViewSource extends React.Component<IProps, IState> {
         };
         if (isEncrypted) {
             const copyDecryptedFunc = (): string => {
-                return stringify(decryptedEventSource);
+                return stringify(decryptedEventSource || {});
             };
             return (
                 <>
@@ -117,7 +117,7 @@ export default class ViewSource extends React.Component<IProps, IState> {
             return (
                 <MatrixClientContext.Consumer>
                     {(cli) => (
-                        <DevtoolsContext.Provider value={{ room: cli.getRoom(roomId) }}>
+                        <DevtoolsContext.Provider value={{ room: cli.getRoom(roomId)! }}>
                             <StateEventEditor onBack={this.onBack} mxEvent={mxEvent} />
                         </DevtoolsContext.Provider>
                     )}
@@ -128,7 +128,7 @@ export default class ViewSource extends React.Component<IProps, IState> {
         return (
             <MatrixClientContext.Consumer>
                 {(cli) => (
-                    <DevtoolsContext.Provider value={{ room: cli.getRoom(roomId) }}>
+                    <DevtoolsContext.Provider value={{ room: cli.getRoom(roomId)! }}>
                         <TimelineEventEditor onBack={this.onBack} mxEvent={mxEvent} />
                     </DevtoolsContext.Provider>
                 )}

src/components/structures/auth/ForgotPassword.tsx

@@ -395,7 +395,7 @@ export default class ForgotPassword extends React.Component<Props, State> {
             button: _t("Continue"),
         });
         const [confirmed] = await finished;
-        return confirmed;
+        return !!confirmed;
     }
 
     public renderCheckEmail(): JSX.Element {

src/components/structures/auth/Login.tsx

@@ -368,7 +368,7 @@ export default class LoginComponent extends React.PureComponent<IProps, IState>
             isDefaultServer = true;
         }
 
-        const fallbackHsUrl = isDefaultServer ? this.props.fallbackHsUrl : null;
+        const fallbackHsUrl = isDefaultServer ? this.props.fallbackHsUrl! : null;
 
         const loginLogic = new Login(hsUrl, isUrl, fallbackHsUrl, {
             defaultDeviceDisplayName: this.props.defaultDeviceDisplayName,
@@ -514,7 +514,7 @@ export default class LoginComponent extends React.PureComponent<IProps, IState>
         // this is the ideal order we want to show the flows in
         const order = ["m.login.password", "m.login.sso"];
 
-        const flows = filterBoolean(order.map((type) => this.state.flows.find((flow) => flow.type === type)));
+        const flows = filterBoolean(order.map((type) => this.state.flows?.find((flow) => flow.type === type)));
         return (
             <React.Fragment>
                 {flows.map((flow) => {
@@ -546,7 +546,7 @@ export default class LoginComponent extends React.PureComponent<IProps, IState>
     };
 
     private renderSsoStep = (loginType: "cas" | "sso"): JSX.Element => {
-        const flow = this.state.flows.find((flow) => flow.type === "m.login." + loginType) as ISSOFlow;
+        const flow = this.state.flows?.find((flow) => flow.type === "m.login." + loginType) as ISSOFlow;
 
         return (
             <SSOButtons
@@ -554,7 +554,7 @@ export default class LoginComponent extends React.PureComponent<IProps, IState>
                 flow={flow}
                 loginType={loginType}
                 fragmentAfterLogin={this.props.fragmentAfterLogin}
-                primary={!this.state.flows.find((flow) => flow.type === "m.login.password")}
+                primary={!this.state.flows?.find((flow) => flow.type === "m.login.password")}
                 action={SSOAction.LOGIN}
             />
         );

src/components/structures/auth/SetupEncryptionBody.tsx

@@ -88,7 +88,7 @@ export default class SetupEncryptionBody extends React.Component<IProps, IState>
 
     private onVerifyClick = (): void => {
         const cli = MatrixClientPeg.get();
-        const userId = cli.getUserId();
+        const userId = cli.getSafeUserId();
         const requestPromise = cli.requestVerification(userId);
 
         // We need to call onFinished now to close this dialog, and
@@ -212,7 +212,7 @@ export default class SetupEncryptionBody extends React.Component<IProps, IState>
                             {useRecoveryKeyButton}
                         </div>
                         <div className="mx_SetupEncryptionBody_reset">
-                            {_t("Forgotten or lost all recovery methods? <a>Reset all</a>", null, {
+                            {_t("Forgotten or lost all recovery methods? <a>Reset all</a>", undefined, {
                                 a: (sub) => (
                                     <AccessibleButton
                                         kind="link_inline"
@@ -228,7 +228,7 @@ export default class SetupEncryptionBody extends React.Component<IProps, IState>
                 );
             }
         } else if (phase === Phase.Done) {
-            let message;
+            let message: JSX.Element;
             if (this.state.backupInfo) {
                 message = (
                     <p>

src/components/structures/auth/SoftLogout.tsx

@@ -23,7 +23,7 @@ import { _t } from "../../../languageHandler";
 import dis from "../../../dispatcher/dispatcher";
 import * as Lifecycle from "../../../Lifecycle";
 import Modal from "../../../Modal";
-import { MatrixClientPeg } from "../../../MatrixClientPeg";
+import { IMatrixClientCreds, MatrixClientPeg } from "../../../MatrixClientPeg";
 import { sendLoginRequest } from "../../../Login";
 import AuthPage from "../../views/auth/AuthPage";
 import { SSO_HOMESERVER_URL_KEY, SSO_ID_SERVER_URL_KEY } from "../../../BasePlatform";
@@ -159,7 +159,7 @@ export default class SoftLogout extends React.Component<IProps, IState> {
             device_id: MatrixClientPeg.get().getDeviceId(),
         };
 
-        let credentials = null;
+        let credentials: IMatrixClientCreds;
         try {
             credentials = await sendLoginRequest(hsUrl, isUrl, loginType, loginParams);
         } catch (e) {
@@ -192,7 +192,7 @@ export default class SoftLogout extends React.Component<IProps, IState> {
             device_id: MatrixClientPeg.get().getDeviceId(),
         };
 
-        let credentials = null;
+        let credentials: IMatrixClientCreds;
         try {
             credentials = await sendLoginRequest(hsUrl, isUrl, loginType, loginParams);
         } catch (e) {
@@ -212,7 +212,7 @@ export default class SoftLogout extends React.Component<IProps, IState> {
     }
 
     private renderPasswordForm(introText: Optional<string>): JSX.Element {
-        let error: JSX.Element = null;
+        let error: JSX.Element | undefined;
         if (this.state.errorText) {
             error = <span className="mx_Login_error">{this.state.errorText}</span>;
         }
@@ -267,7 +267,7 @@ export default class SoftLogout extends React.Component<IProps, IState> {
             return <Spinner />;
         }
 
-        let introText = null; // null is translated to something area specific in this function
+        let introText: string | null = null; // null is translated to something area specific in this function
         if (this.state.keyBackupNeeded) {
             introText = _t(
                 "Regain access to your account and recover encryption keys stored in this session. " +

src/components/structures/auth/header/AuthHeaderDisplay.tsx

@@ -27,7 +27,7 @@ interface Props {
 export function AuthHeaderDisplay({ title, icon, serverPicker, children }: PropsWithChildren<Props>): JSX.Element {
     const context = useContext(AuthHeaderContext);
     if (!context) {
-        return null;
+        return <></>;
     }
     const current = context.state.length ? context.state[0] : null;
     return (

src/components/views/context_menus/RoomContextMenu.tsx

@@ -61,7 +61,7 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
         RoomListStore.instance.getTagsForRoom(room),
     );
 
-    let leaveOption: JSX.Element;
+    let leaveOption: JSX.Element | undefined;
     if (roomTags.includes(DefaultTagID.Archived)) {
         const onForgetRoomClick = (ev: ButtonEvent): void => {
             ev.preventDefault();
@@ -112,7 +112,7 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
     const isVideoRoom =
         videoRoomsEnabled && (room.isElementVideoRoom() || (elementCallVideoRoomsEnabled && room.isCallRoom()));
 
-    let inviteOption: JSX.Element;
+    let inviteOption: JSX.Element | undefined;
     if (room.canInvite(cli.getUserId()!) && !isDm) {
         const onInviteClick = (ev: ButtonEvent): void => {
             ev.preventDefault();
@@ -136,9 +136,9 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
         );
     }
 
-    let favouriteOption: JSX.Element;
+    let favouriteOption: JSX.Element | undefined;
-    let lowPriorityOption: JSX.Element;
+    let lowPriorityOption: JSX.Element | undefined;
-    let notificationOption: JSX.Element;
+    let notificationOption: JSX.Element | undefined;
     if (room.getMyMembership() === "join") {
         const isFavorite = roomTags.includes(DefaultTagID.Favourite);
         favouriteOption = (
@@ -208,8 +208,8 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
         );
     }
 
-    let peopleOption: JSX.Element;
+    let peopleOption: JSX.Element | undefined;
-    let copyLinkOption: JSX.Element;
+    let copyLinkOption: JSX.Element | undefined;
     if (!isDm) {
         peopleOption = (
             <IconizedContextMenuOption
@@ -247,7 +247,7 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
         );
     }
 
-    let filesOption: JSX.Element;
+    let filesOption: JSX.Element | undefined;
     if (!isVideoRoom) {
         filesOption = (
             <IconizedContextMenuOption
@@ -266,9 +266,9 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
     }
 
     const pinningEnabled = useFeatureEnabled("feature_pinning");
-    const pinCount = usePinnedEvents(pinningEnabled && room)?.length;
+    const pinCount = usePinnedEvents(pinningEnabled ? room : undefined)?.length;
 
-    let pinsOption: JSX.Element;
+    let pinsOption: JSX.Element | undefined;
     if (pinningEnabled && !isVideoRoom) {
         pinsOption = (
             <IconizedContextMenuOption
@@ -288,7 +288,7 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
         );
     }
 
-    let widgetsOption: JSX.Element;
+    let widgetsOption: JSX.Element | undefined;
     if (!isVideoRoom) {
         widgetsOption = (
             <IconizedContextMenuOption
@@ -306,7 +306,7 @@ const RoomContextMenu: React.FC<IProps> = ({ room, onFinished, ...props }) => {
         );
     }
 
-    let exportChatOption: JSX.Element;
+    let exportChatOption: JSX.Element | undefined;
     if (!isVideoRoom) {
         exportChatOption = (
             <IconizedContextMenuOption

src/components/views/dialogs/AddExistingToSpaceDialog.tsx

@@ -40,6 +40,7 @@ import DecoratedRoomAvatar from "../avatars/DecoratedRoomAvatar";
 import QueryMatcher from "../../../autocomplete/QueryMatcher";
 import LazyRenderList from "../elements/LazyRenderList";
 import { useSettingValue } from "../../../hooks/useSettings";
+import { filterBoolean } from "../../../utils/arrays";
 
 // These values match CSS
 const ROW_HEIGHT = 32 + 12;
@@ -56,7 +57,7 @@ interface IProps {
 export const Entry: React.FC<{
     room: Room;
     checked: boolean;
-    onChange(value: boolean): void;
+    onChange?(value: boolean): void;
 }> = ({ room, checked, onChange }) => {
     return (
         <label className="mx_AddExistingToSpace_entry">
@@ -67,7 +68,7 @@ export const Entry: React.FC<{
             )}
             <span className="mx_AddExistingToSpace_entry_name">{room.name}</span>
             <StyledCheckbox
-                onChange={onChange ? (e) => onChange(e.currentTarget.checked) : null}
+                onChange={onChange ? (e) => onChange(e.currentTarget.checked) : undefined}
                 checked={checked}
                 disabled={!onChange}
             />
@@ -150,8 +151,8 @@ export const AddExistingToSpace: React.FC<IAddExistingToSpaceProps> = ({
     });
 
     const [selectedToAdd, setSelectedToAdd] = useState(new Set<Room>());
-    const [progress, setProgress] = useState<number>(null);
+    const [progress, setProgress] = useState<number | null>(null);
-    const [error, setError] = useState<Error>(null);
+    const [error, setError] = useState<Error | null>(null);
     const [query, setQuery] = useState("");
     const lcQuery = query.toLowerCase().trim();
 
@@ -164,7 +165,7 @@ export const AddExistingToSpace: React.FC<IAddExistingToSpaceProps> = ({
         if (lcQuery) {
             const matcher = new QueryMatcher<Room>(visibleRooms, {
                 keys: ["name"],
-                funcs: [(r) => [r.getCanonicalAlias(), ...r.getAltAliases()].filter(Boolean)],
+                funcs: [(r) => filterBoolean([r.getCanonicalAlias(), ...r.getAltAliases()])],
                 shouldMatchWordsOnly: false,
             });
 
@@ -172,7 +173,7 @@ export const AddExistingToSpace: React.FC<IAddExistingToSpaceProps> = ({
         }
 
         const joinRule = space.getJoinRule();
-        return sortRooms(rooms).reduce(
+        return sortRooms(rooms).reduce<[spaces: Room[], rooms: Room[], dms: Room[]]>(
             (arr, room) => {
                 if (room.isSpaceRoom()) {
                     if (room !== space && !existingSubspacesSet.has(room)) {
@@ -289,7 +290,7 @@ export const AddExistingToSpace: React.FC<IAddExistingToSpaceProps> = ({
                   }
                   setSelectedToAdd(new Set(selectedToAdd));
               }
-            : null;
+            : undefined;
 
     // only count spaces when alone as they're shown on a separate modal all on their own
     const numSpaces = spacesRenderer && !dmsRenderer && !roomsRenderer ? spaces.length : 0;
@@ -373,7 +374,7 @@ const defaultRendererFactory =
                                     ? (checked: boolean) => {
                                           onChange(checked, room);
                                       }
-                                    : null
+                                    : undefined
                             }
                         />
                     )}
@@ -397,7 +398,7 @@ export const SubspaceSelector: React.FC<ISubspaceSelectorProps> = ({ title, spac
         return [
             space,
             ...SpaceStore.instance.getChildSpaces(space.roomId).filter((space) => {
-                return space.currentState.maySendStateEvent(EventType.SpaceChild, space.client.credentials.userId);
+                return space.currentState.maySendStateEvent(EventType.SpaceChild, space.client.getSafeUserId());
             }),
         ];
     }, [space]);

src/components/views/dialogs/BaseDialog.tsx

@@ -153,12 +153,11 @@ export default class BaseDialog extends React.Component<IProps> {
 
         return (
             <MatrixClientContext.Provider value={this.matrixClient}>
-                <PosthogScreenTracker screenName={this.props.screenName} />
+                {this.props.screenName && <PosthogScreenTracker screenName={this.props.screenName} />}
                 <FocusLock
                     returnFocus={true}
                     lockProps={lockProps}
-                    className={classNames({
+                    className={classNames(this.props.className, {
-                        [this.props.className]: true,
                         mx_Dialog_fixedWidth: this.props.fixedWidth,
                     })}
                 >

src/components/views/dialogs/InviteDialog.tsx

@@ -74,6 +74,7 @@ import { InviteKind } from "./InviteDialogTypes";
 import Modal from "../../../Modal";
 import dis from "../../../dispatcher/dispatcher";
 import { privateShouldBeEncrypted } from "../../../utils/rooms";
+import { NonEmptyArray } from "../../../@types/common";
 
 // we have a number of types defined from the Matrix spec which can't reasonably be altered here.
 /* eslint-disable camelcase */
@@ -1421,10 +1422,9 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
 
         let dialogContent;
         if (this.props.kind === InviteKind.CallTransfer) {
-            const tabs: Tab[] = [];
+            const tabs: NonEmptyArray<Tab> = [
-            tabs.push(
                 new Tab(TabId.UserDirectory, _td("User Directory"), "mx_InviteDialog_userDirectoryIcon", usersSection),
-            );
+            ];
 
             const backspaceButton = <DialPadBackspaceButton onBackspacePress={this.onDeletePress} />;
 

src/components/views/dialogs/RoomSettingsDialog.tsx

@@ -34,6 +34,7 @@ import BaseDialog from "./BaseDialog";
 import { Action } from "../../../dispatcher/actions";
 import { VoipRoomSettingsTab } from "../settings/tabs/room/VoipRoomSettingsTab";
 import { ActionPayload } from "../../../dispatcher/payloads";
+import { NonEmptyArray } from "../../../@types/common";
 
 export const ROOM_GENERAL_TAB = "ROOM_GENERAL_TAB";
 export const ROOM_VOIP_TAB = "ROOM_VOIP_TAB";
@@ -85,11 +86,11 @@ export default class RoomSettingsDialog extends React.Component<IProps, IState>
 
     private onRoomName = (): void => {
         this.setState({
-            roomName: MatrixClientPeg.get().getRoom(this.props.roomId).name,
+            roomName: MatrixClientPeg.get().getRoom(this.props.roomId)?.name ?? "",
         });
     };
 
-    private getTabs(): Tab[] {
+    private getTabs(): NonEmptyArray<Tab> {
         const tabs: Tab[] = [];
 
         tabs.push(
@@ -178,7 +179,7 @@ export default class RoomSettingsDialog extends React.Component<IProps, IState>
             );
         }
 
-        return tabs;
+        return tabs as NonEmptyArray<Tab>;
     }
 
     public render(): React.ReactNode {

src/components/views/dialogs/SpacePreferencesDialog.tsx

@@ -26,6 +26,7 @@ import SettingsStore from "../../../settings/SettingsStore";
 import { SettingLevel } from "../../../settings/SettingLevel";
 import RoomName from "../elements/RoomName";
 import { SpacePreferenceTab } from "../../../dispatcher/payloads/OpenSpacePreferencesPayload";
+import { NonEmptyArray } from "../../../@types/common";
 
 interface IProps {
     space: Room;
@@ -69,7 +70,7 @@ const SpacePreferencesAppearanceTab: React.FC<Pick<IProps, "space">> = ({ space
 };
 
 const SpacePreferencesDialog: React.FC<IProps> = ({ space, initialTabId, onFinished }) => {
-    const tabs = [
+    const tabs: NonEmptyArray<Tab> = [
         new Tab(
             SpacePreferenceTab.Appearance,
             _td("Appearance"),

src/components/views/dialogs/SpaceSettingsDialog.tsx

@@ -30,6 +30,7 @@ import { UIFeature } from "../../../settings/UIFeature";
 import AdvancedRoomSettingsTab from "../settings/tabs/room/AdvancedRoomSettingsTab";
 import RolesRoomSettingsTab from "../settings/tabs/room/RolesRoomSettingsTab";
 import { Action } from "../../../dispatcher/actions";
+import { NonEmptyArray } from "../../../@types/common";
 
 export enum SpaceSettingsTab {
     General = "SPACE_GENERAL_TAB",
@@ -79,7 +80,7 @@ const SpaceSettingsDialog: React.FC<IProps> = ({ matrixClient: cli, space, onFin
                       <AdvancedRoomSettingsTab roomId={space.roomId} closeSettingsFn={onFinished} />,
                   )
                 : null,
-        ].filter(Boolean);
+        ].filter(Boolean) as NonEmptyArray<Tab>;
     }, [cli, space, onFinished]);
 
     return (

src/components/views/dialogs/UserSettingsDialog.tsx

@@ -36,6 +36,7 @@ import SidebarUserSettingsTab from "../settings/tabs/user/SidebarUserSettingsTab
 import KeyboardUserSettingsTab from "../settings/tabs/user/KeyboardUserSettingsTab";
 import SessionManagerTab from "../settings/tabs/user/SessionManagerTab";
 import { UserTab } from "./UserTab";
+import { NonEmptyArray } from "../../../@types/common";
 
 interface IProps {
     initialTabId?: UserTab;
@@ -80,7 +81,7 @@ export default class UserSettingsDialog extends React.Component<IProps, IState>
         this.setState({ newSessionManagerEnabled: newValue });
     };
 
-    private getTabs(): Tab[] {
+    private getTabs(): NonEmptyArray<Tab> {
         const tabs: Tab[] = [];
 
         tabs.push(
@@ -207,7 +208,7 @@ export default class UserSettingsDialog extends React.Component<IProps, IState>
             ),
         );
 
-        return tabs;
+        return tabs as NonEmptyArray<Tab>;
     }
 
     public render(): React.ReactNode {

src/components/views/elements/DesktopCapturerSourcePicker.tsx

@@ -23,6 +23,7 @@ import DialogButtons from "./DialogButtons";
 import AccessibleButton from "./AccessibleButton";
 import TabbedView, { Tab, TabLocation } from "../../structures/TabbedView";
 import PlatformPeg from "../../../PlatformPeg";
+import { NonEmptyArray } from "../../../@types/common";
 
 export function getDesktopCapturerSources(): Promise<Array<DesktopCapturerSource>> {
     const options: GetSourcesOptions = {
@@ -80,7 +81,7 @@ export interface PickerIState {
     selectedSource: DesktopCapturerSource | null;
 }
 export interface PickerIProps {
-    onFinished(sourceId: string): void;
+    onFinished(sourceId?: string): void;
 }
 
 export default class DesktopCapturerSourcePicker extends React.Component<PickerIProps, PickerIState> {
@@ -129,7 +130,7 @@ export default class DesktopCapturerSourcePicker extends React.Component<PickerI
     };
 
     private onCloseClick = (): void => {
-        this.props.onFinished(null);
+        this.props.onFinished();
     };
 
     private getTab(type: "screen" | "window", label: string): Tab {
@@ -150,7 +151,7 @@ export default class DesktopCapturerSourcePicker extends React.Component<PickerI
     }
 
     public render(): React.ReactNode {
-        const tabs = [
+        const tabs: NonEmptyArray<Tab> = [
             this.getTab("screen", _t("Share entire screen")),
             this.getTab("window", _t("Application window")),
         ];

src/components/views/elements/PowerSelector.tsx

@@ -25,7 +25,7 @@ import { objectHasDiff } from "../../../utils/objects";
 
 const CUSTOM_VALUE = "SELECT_VALUE_CUSTOM";
 
-interface IProps {
+interface Props<K extends undefined | string> {
     value: number;
     // The maximum value that can be set with the power selector
     maxValue: number;
@@ -35,13 +35,14 @@ interface IProps {
 
     // should the user be able to change the value? false by default.
     disabled?: boolean;
-    onChange?: (value: number, powerLevelKey: string) => void;
-
-    // Optional key to pass as the second argument to `onChange`
-    powerLevelKey?: string;
 
     // The name to annotate the selector with
     label?: string;
+
+    onChange(value: number, powerLevelKey: K extends undefined ? void : K): void;
+
+    // Optional key to pass as the second argument to `onChange`
+    powerLevelKey: K extends undefined ? void : K;
 }
 
 interface IState {
@@ -54,13 +55,13 @@ interface IState {
     custom?: boolean;
 }
 
-export default class PowerSelector extends React.Component<IProps, IState> {
+export default class PowerSelector<K extends undefined | string> extends React.Component<Props<K>, IState> {
-    public static defaultProps: Partial<IProps> = {
+    public static defaultProps: Partial<Props<any>> = {
         maxValue: Infinity,
         usersDefault: 0,
     };
 
-    public constructor(props: IProps) {
+    public constructor(props: Props<K>) {
         super(props);
 
         this.state = {
@@ -77,7 +78,7 @@ export default class PowerSelector extends React.Component<IProps, IState> {
         this.initStateFromProps();
     }
 
-    public componentDidUpdate(prevProps: Readonly<IProps>): void {
+    public componentDidUpdate(prevProps: Readonly<Props<K>>): void {
         if (objectHasDiff(this.props, prevProps)) {
             this.initStateFromProps();
         }

src/components/views/elements/QRCode.tsx

@@ -31,7 +31,7 @@ const defaultOptions: QRCodeToDataURLOptions = {
 };
 
 const QRCode: React.FC<IProps> = ({ data, className, ...options }) => {
-    const [dataUri, setUri] = React.useState<string>(null);
+    const [dataUri, setUri] = React.useState<string | null>(null);
     React.useEffect(() => {
         let cancelled = false;
         toDataURL(data, { ...defaultOptions, ...options }).then((uri) => {

src/components/views/elements/ReplyChain.tsx

@@ -63,7 +63,7 @@ interface IState {
     // The loaded events to be rendered as linear-replies
     events: MatrixEvent[];
     // The latest loaded event which has not yet been shown
-    loadedEv: MatrixEvent;
+    loadedEv: MatrixEvent | null;
     // Whether the component is still loading more events
     loading: boolean;
     // Whether as error was encountered fetching a replied to event.
@@ -145,7 +145,7 @@ export default class ReplyChain extends React.Component<IProps, IState> {
         }
     }
 
-    private async getNextEvent(ev: MatrixEvent): Promise<MatrixEvent> {
+    private async getNextEvent(ev: MatrixEvent): Promise<MatrixEvent | null> {
         try {
             const inReplyToEventId = getParentEventId(ev);
             return await this.getEvent(inReplyToEventId);
@@ -154,7 +154,7 @@ export default class ReplyChain extends React.Component<IProps, IState> {
         }
     }
 
-    private async getEvent(eventId: string): Promise<MatrixEvent> {
+    private async getEvent(eventId: string): Promise<MatrixEvent | null> {
         if (!eventId) return null;
         const event = this.room.findEventById(eventId);
         if (event) return event;
@@ -168,7 +168,7 @@ export default class ReplyChain extends React.Component<IProps, IState> {
             // Return null as it is falsy and thus should be treated as an error (as the event cannot be resolved).
             return null;
         }
-        return this.room.findEventById(eventId);
+        return this.room.findEventById(eventId) ?? null;
     }
 
     public canCollapse = (): boolean => {
@@ -182,7 +182,7 @@ export default class ReplyChain extends React.Component<IProps, IState> {
     private onQuoteClick = async (event: ButtonEvent): Promise<void> => {
         const events = [this.state.loadedEv, ...this.state.events];
 
-        let loadedEv = null;
+        let loadedEv: MatrixEvent | null = null;
         if (events.length > 0) {
             loadedEv = await this.getNextEvent(events[0]);
         }
@@ -200,7 +200,7 @@ export default class ReplyChain extends React.Component<IProps, IState> {
     }
 
     public render(): React.ReactNode {
-        let header = null;
+        let header: JSX.Element | undefined;
         if (this.state.err) {
             header = (
                 <blockquote className="mx_ReplyChain mx_ReplyChain_error">

src/components/views/elements/Slider.tsx

@@ -81,7 +81,7 @@ export default class Slider extends React.Component<IProps> {
             />
         ));
 
-        let selection = null;
+        let selection: JSX.Element | undefined;
 
         if (!this.props.disabled) {
             const offset = this.offset(this.props.values, this.props.value);

src/components/views/elements/TruncatedList.tsx

@@ -21,7 +21,7 @@ import { _t } from "../../../languageHandler";
 
 interface IProps {
     // The number of elements to show before truncating. If negative, no truncation is done.
-    truncateAt?: number;
+    truncateAt: number;
     // The className to apply to the wrapping div
     className?: string;
     // A function that returns the children to be rendered into the element.
@@ -34,7 +34,7 @@ interface IProps {
     getChildCount?: () => number;
     // A function which will be invoked when an overflow element is required.
     // This will be inserted after the children.
-    createOverflowElement?: (overflowCount: number, totalCount: number) => React.ReactNode;
+    createOverflowElement: (overflowCount: number, totalCount: number) => React.ReactNode;
     children?: ReactNode;
 }
 
@@ -71,8 +71,8 @@ export default class TruncatedList extends React.Component<IProps> {
         }
     }
 
-    public render(): React.ReactNode {
+    public render(): ReactNode {
-        let overflowNode = null;
+        let overflowNode: ReactNode | undefined;
 
         const totalChildren = this.getChildCount();
         let upperBound = totalChildren;

src/components/views/right_panel/PinnedMessagesCard.tsx

@@ -37,6 +37,7 @@ import RoomContext, { TimelineRenderingType } from "../../../contexts/RoomContex
 import { ReadPinsEventId } from "./types";
 import Heading from "../typography/Heading";
 import { RoomPermalinkCreator } from "../../../utils/permalinks/Permalinks";
+import { filterBoolean } from "../../../utils/arrays";
 
 interface IProps {
     room: Room;
@@ -44,7 +45,7 @@ interface IProps {
     onClose(): void;
 }
 
-export const usePinnedEvents = (room: Room): string[] => {
+export const usePinnedEvents = (room?: Room): string[] => {
     const [pinnedEvents, setPinnedEvents] = useState<string[]>([]);
 
     const update = useCallback(
@@ -173,8 +174,7 @@ const PinnedMessagesCard: React.FC<IProps> = ({ room, onClose, permalinkCreator
         };
 
         // show them in reverse, with latest pinned at the top
-        content = pinnedEvents
+        content = filterBoolean(pinnedEvents)
-            .filter(Boolean)
             .reverse()
             .map((ev) => (
                 <PinnedEventTile

src/components/views/right_panel/RoomSummaryCard.tsx

@@ -325,7 +325,7 @@ const RoomSummaryCard: React.FC<IProps> = ({ room, permalinkCreator, onClose })
 
     const memberCount = useRoomMemberCount(room);
     const pinningEnabled = useFeatureEnabled("feature_pinning");
-    const pinCount = usePinnedEvents(pinningEnabled && room)?.length;
+    const pinCount = usePinnedEvents(pinningEnabled ? room : undefined)?.length;
 
     const isPollHistoryEnabled = useFeatureEnabled("feature_poll_history");
 

src/components/views/rooms/E2EIcon.tsx

@@ -44,7 +44,7 @@ const crossSigningRoomTitles: { [key in E2EState]?: string } = {
 
 interface IProps {
     isUser?: boolean;
-    status?: E2EState | E2EStatus;
+    status: E2EState | E2EStatus;
     className?: string;
     size?: number;
     onClick?: () => void;
@@ -76,7 +76,7 @@ const E2EIcon: React.FC<IProps> = ({
         className,
     );
 
-    let e2eTitle;
+    let e2eTitle: string | undefined;
     if (isUser) {
         e2eTitle = crossSigningUserTitles[status];
     } else {

src/components/views/rooms/EntityTile.tsx

@@ -43,7 +43,7 @@ const PRESENCE_CLASS: Record<PresenceState, string> = {
     unavailable: "mx_EntityTile_unavailable",
 };
 
-function presenceClassForMember(presenceState: PresenceState, lastActiveAgo: number, showPresence: boolean): string {
+function presenceClassForMember(presenceState?: PresenceState, lastActiveAgo?: number, showPresence?: boolean): string {
     if (showPresence === false) {
         return "mx_EntityTile_online_beenactive";
     }
@@ -74,7 +74,7 @@ interface IProps {
     presenceLastTs?: number;
     presenceCurrentlyActive?: boolean;
     showInviteButton?: boolean;
-    onClick?(): void;
+    onClick(): void;
     suppressOnHover?: boolean;
     showPresence?: boolean;
     subtextLabel?: string;
@@ -108,7 +108,7 @@ export default class EntityTile extends React.PureComponent<IProps, IState> {
     public render(): React.ReactNode {
         const mainClassNames: Record<string, boolean> = {
             mx_EntityTile: true,
-            mx_EntityTile_noHover: this.props.suppressOnHover,
+            mx_EntityTile_noHover: !!this.props.suppressOnHover,
         };
         if (this.props.className) mainClassNames[this.props.className] = true;
 
@@ -127,7 +127,7 @@ export default class EntityTile extends React.PureComponent<IProps, IState> {
                 ? Date.now() - (this.props.presenceLastTs - this.props.presenceLastActiveAgo)
                 : -1;
 
-            let presenceLabel = null;
+            let presenceLabel: JSX.Element | undefined;
             if (this.props.showPresence) {
                 presenceLabel = (
                     <PresenceLabel

src/components/views/rooms/PresenceLabel.tsx

@@ -39,7 +39,7 @@ export default class PresenceLabel extends React.Component<IProps> {
 
     // Return duration as a string using appropriate time units
     // XXX: This would be better handled using a culture-aware library, but we don't use one yet.
-    private getDuration(time: number): string {
+    private getDuration(time: number): string | undefined {
         if (!time) return;
         const t = Math.round(time / 1000);
         const s = t % 60;
@@ -61,11 +61,11 @@ export default class PresenceLabel extends React.Component<IProps> {
         return _t("%(duration)sd", { duration: d });
     }
 
-    private getPrettyPresence(presence: string, activeAgo: number, currentlyActive: boolean): string {
+    private getPrettyPresence(presence?: string, activeAgo?: number, currentlyActive?: boolean): string {
         // for busy presence, we ignore the 'currentlyActive' flag: they're busy whether
         // they're active or not. It can be set while the user is active in which case
         // the 'active ago' ends up being 0.
-        if (BUSY_PRESENCE_NAME.matches(presence)) return _t("Busy");
+        if (presence && BUSY_PRESENCE_NAME.matches(presence)) return _t("Busy");
 
         if (!currentlyActive && activeAgo !== undefined && activeAgo > 0) {
             const duration = this.getDuration(activeAgo);

src/components/views/settings/account/PhoneNumbers.tsx

@@ -129,9 +129,9 @@ interface IProps {
 
 interface IState {
     verifying: boolean;
-    verifyError: string;
+    verifyError: string | null;
     verifyMsisdn: string;
-    addTask: AddThreepid;
+    addTask: AddThreepid | null;
     continueDisabled: boolean;
     phoneCountry: string;
     newPhoneNumber: string;
@@ -205,7 +205,7 @@ export default class PhoneNumbers extends React.Component<IProps, IState> {
         const token = this.state.newPhoneNumberCode;
         const address = this.state.verifyMsisdn;
         this.state.addTask
-            .haveMsisdnToken(token)
+            ?.haveMsisdnToken(token)
             .then(([finished]) => {
                 let newPhoneNumber = this.state.newPhoneNumber;
                 if (finished) {

src/components/views/settings/tabs/room/RolesRoomSettingsTab.tsx

@@ -21,6 +21,7 @@ import { RoomState, RoomStateEvent } from "matrix-js-sdk/src/models/room-state";
 import { logger } from "matrix-js-sdk/src/logger";
 import { throttle, get } from "lodash";
 import { compare } from "matrix-js-sdk/src/utils";
+import { IContent } from "matrix-js-sdk/src/models/event";
 
 import { _t, _td } from "../../../../../languageHandler";
 import { MatrixClientPeg } from "../../../../../MatrixClientPeg";
@@ -171,8 +172,8 @@ export default class RolesRoomSettingsTab extends React.Component<IProps> {
     private onPowerLevelsChanged = (value: number, powerLevelKey: string): void => {
         const client = MatrixClientPeg.get();
         const room = client.getRoom(this.props.roomId);
-        const plEvent = room.currentState.getStateEvents(EventType.RoomPowerLevels, "");
+        const plEvent = room?.currentState.getStateEvents(EventType.RoomPowerLevels, "");
-        let plContent = plEvent ? plEvent.getContent() || {} : {};
+        let plContent = plEvent?.getContent() ?? {};
 
         // Clone the power levels just in case
         plContent = Object.assign({}, plContent);
@@ -185,7 +186,7 @@ export default class RolesRoomSettingsTab extends React.Component<IProps> {
             plContent["events"][powerLevelKey.slice(eventsLevelPrefix.length)] = value;
         } else {
             const keyPath = powerLevelKey.split(".");
-            let parentObj;
+            let parentObj: IContent | undefined;
             let currentObj = plContent;
             for (const key of keyPath) {
                 if (!currentObj[key]) {
@@ -213,8 +214,8 @@ export default class RolesRoomSettingsTab extends React.Component<IProps> {
     private onUserPowerLevelChanged = (value: number, powerLevelKey: string): void => {
         const client = MatrixClientPeg.get();
         const room = client.getRoom(this.props.roomId);
-        const plEvent = room.currentState.getStateEvents(EventType.RoomPowerLevels, "");
+        const plEvent = room?.currentState.getStateEvents(EventType.RoomPowerLevels, "");
-        let plContent = plEvent ? plEvent.getContent() || {} : {};
+        let plContent = plEvent?.getContent() ?? {};
 
         // Clone the power levels just in case
         plContent = Object.assign({}, plContent);

src/stores/WidgetStore.ts

@@ -113,7 +113,7 @@ export default class WidgetStore extends AsyncStoreWithClient<IState> {
         });
     }
 
-    private loadRoomWidgets(room: Room): void {
+    private loadRoomWidgets(room: Room | null): void {
         if (!room) return;
         const roomInfo = this.roomMap.get(room.roomId) || <IRoomWidgets>{};
         roomInfo.widgets = [];

src/utils/localRoom/isLocalRoom.ts

@@ -18,7 +18,7 @@ import { Room } from "matrix-js-sdk/src/matrix";
 
 import { LocalRoom, LOCAL_ROOM_ID_PREFIX } from "../../models/LocalRoom";
 
-export function isLocalRoom(roomOrID: Room | string): boolean {
+export function isLocalRoom(roomOrID?: Room | string): boolean {
     if (typeof roomOrID === "string") {
         return roomOrID.startsWith(LOCAL_ROOM_ID_PREFIX);
     }

test/components/structures/TabbedView-test.tsx

@@ -18,6 +18,7 @@ import React from "react";
 import { act, fireEvent, render } from "@testing-library/react";
 
 import TabbedView, { Tab, TabLocation } from "../../../src/components/structures/TabbedView";
+import { NonEmptyArray } from "../../../src/@types/common";
 
 describe("<TabbedView />", () => {
     const generalTab = new Tab("GENERAL", "General", "general", <div>general</div>);
@@ -25,7 +26,7 @@ describe("<TabbedView />", () => {
     const securityTab = new Tab("SECURITY", "Security", "security", <div>security</div>);
     const defaultProps = {
         tabLocation: TabLocation.LEFT,
-        tabs: [generalTab, labsTab, securityTab],
+        tabs: [generalTab, labsTab, securityTab] as NonEmptyArray<Tab>,
     };
     const getComponent = (props = {}): React.ReactElement => <TabbedView {...defaultProps} {...props} />;
 
@@ -58,11 +59,6 @@ describe("<TabbedView />", () => {
         expect(getActiveTabBody(container)?.textContent).toEqual("security");
     });
 
-    it("renders without error when there are no tabs", () => {
-        const { container } = render(getComponent({ tabs: [] }));
-        expect(container).toMatchSnapshot();
-    });
-
     it("sets active tab on tab click", () => {
         const { container, getByTestId } = render(getComponent());
 

test/components/structures/__snapshots__/TabbedView-test.tsx.snap

@@ -69,15 +69,3 @@ exports[`<TabbedView /> renders tabs 1`] = `
   </div>
 </div>
 `;
-
-exports[`<TabbedView /> renders without error when there are no tabs 1`] = `
-<div>
-  <div
-    class="mx_TabbedView mx_TabbedView_tabsOnLeft"
-  >
-    <div
-      class="mx_TabbedView_tabLabels"
-    />
-  </div>
-</div>
-`;

test/components/views/dialogs/polls/__snapshots__/PollHistoryDialog-test.tsx.snap

@@ -38,7 +38,7 @@ exports[`<PollHistoryDialog /> renders a list of active polls when there are pol
   />
   <div
     aria-labelledby="mx_BaseDialog_title"
-    class="undefined mx_Dialog_fixedWidth"
+    class="mx_Dialog_fixedWidth"
     data-focus-lock-disabled="false"
     role="dialog"
   >

test/stores/BreadcrumbsStore-test.ts

@@ -190,8 +190,8 @@ describe("BreadcrumbsStore", () => {
     /**
      * Create as many fake rooms in an array as you ask for.
      */
-    function fakeRooms(howMany: number): Array<Room> {
+    function fakeRooms(howMany: number): Room[] {
-        const ret = [];
+        const ret: Room[] = [];
         for (let i = 0; i < howMany; i++) {
             ret.push(fakeRoom());
         }