Conform more of the codebase to strictNullChecks (#10666)

* Conform more of the codebase to `strictNullChecks`

* Iterate

* Iterate

* Iterate

* Iterate

src/AddThreepid.ts

@@ -293,7 +293,7 @@ export default class AddThreepid {
         const authClient = new IdentityAuthClient();
         const supportsSeparateAddAndBind = await MatrixClientPeg.get().doesServerSupportSeparateAddAndBind();
 
-        let result;
+        let result: { success: boolean } | MatrixError;
         if (this.submitUrl) {
             result = await MatrixClientPeg.get().submitMsisdnTokenOtherUrl(
                 this.submitUrl,
@@ -311,7 +311,7 @@ export default class AddThreepid {
         } else {
             throw new UserFriendlyError("The add / bind with MSISDN flow is misconfigured");
         }
-        if (result.errcode) {
+        if (result instanceof Error) {
             throw result;
         }
 

src/DateUtils.ts

@@ -16,6 +16,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { Optional } from "matrix-events-sdk";
+
 import { _t } from "./languageHandler";
 
 function getDaysArray(): string[] {
@@ -194,10 +196,7 @@ function withinCurrentYear(prevDate: Date, nextDate: Date): boolean {
     return prevDate.getFullYear() === nextDate.getFullYear();
 }
 
-export function wantsDateSeparator(
+export function wantsDateSeparator(prevEventDate: Optional<Date>, nextEventDate: Optional<Date>): boolean {
-    prevEventDate: Date | null | undefined,
-    nextEventDate: Date | null | undefined,
-): boolean {
     if (!nextEventDate || !prevEventDate) {
         return false;
     }

src/LegacyCallHandler.tsx

@@ -288,8 +288,8 @@ export default class LegacyCallHandler extends EventEmitter {
         this.play(AudioID.Ring);
     }
 
-    public isCallSilenced(callId: string): boolean {
+    public isCallSilenced(callId?: string): boolean {
-        return this.isForcedSilent() || this.silencedCalls.has(callId);
+        return this.isForcedSilent() || (!!callId && this.silencedCalls.has(callId));
     }
 
     /**
@@ -395,6 +395,7 @@ export default class LegacyCallHandler extends EventEmitter {
         }
 
         const mappedRoomId = LegacyCallHandler.instance.roomIdForCall(call);
+        if (!mappedRoomId) return;
         if (this.getCallForRoom(mappedRoomId)) {
             logger.log(
                 "Got incoming call for room " + mappedRoomId + " but there's already a call for this room: ignoring",
@@ -411,7 +412,8 @@ export default class LegacyCallHandler extends EventEmitter {
         // the call, we'll be ready to send. NB. This is the protocol-level room ID not
         // the mapped one: that's where we'll send the events.
         const cli = MatrixClientPeg.get();
-        cli.prepareToEncrypt(cli.getRoom(call.roomId));
+        const room = cli.getRoom(call.roomId);
+        if (room) cli.prepareToEncrypt(room);
     };
 
     public getCallById(callId: string): MatrixCall | null {
@@ -505,7 +507,7 @@ export default class LegacyCallHandler extends EventEmitter {
             if (this.audioPromises.has(audioId)) {
                 this.audioPromises.set(
                     audioId,
-                    this.audioPromises.get(audioId).then(() => {
+                    this.audioPromises.get(audioId)!.then(() => {
                         audio.load();
                         return playAudio();
                     }),
@@ -531,7 +533,7 @@ export default class LegacyCallHandler extends EventEmitter {
         };
         if (audio) {
             if (this.audioPromises.has(audioId)) {
-                this.audioPromises.set(audioId, this.audioPromises.get(audioId).then(pauseAudio));
+                this.audioPromises.set(audioId, this.audioPromises.get(audioId)!.then(pauseAudio));
             } else {
                 pauseAudio();
             }
@@ -546,7 +548,7 @@ export default class LegacyCallHandler extends EventEmitter {
         // is the call we consider 'the' call for its room.
         const mappedRoomId = this.roomIdForCall(call);
 
-        const callForThisRoom = this.getCallForRoom(mappedRoomId);
+        const callForThisRoom = mappedRoomId ? this.getCallForRoom(mappedRoomId) : null;
         return !!callForThisRoom && call.callId === callForThisRoom.callId;
     }
 
@@ -840,7 +842,7 @@ export default class LegacyCallHandler extends EventEmitter {
                 cancelButton: _t("OK"),
                 onFinished: (allow) => {
                     SettingsStore.setValue("fallbackICEServerAllowed", null, SettingLevel.DEVICE, allow);
-                    cli.setFallbackICEServerAllowed(allow);
+                    cli.setFallbackICEServerAllowed(!!allow);
                 },
             },
             undefined,
@@ -898,7 +900,7 @@ export default class LegacyCallHandler extends EventEmitter {
         // previous calls that are probably stale by now, so just cancel them.
         if (mappedRoomId !== roomId) {
             const mappedRoom = MatrixClientPeg.get().getRoom(mappedRoomId);
-            if (mappedRoom.getPendingEvents().length > 0) {
+            if (mappedRoom?.getPendingEvents().length) {
                 Resend.cancelUnsentEvents(mappedRoom);
             }
         }
@@ -933,7 +935,7 @@ export default class LegacyCallHandler extends EventEmitter {
         }
     }
 
-    public async placeCall(roomId: string, type?: CallType, transferee?: MatrixCall): Promise<void> {
+    public async placeCall(roomId: string, type: CallType, transferee?: MatrixCall): Promise<void> {
         // Pause current broadcast, if any
         SdkContextClass.instance.voiceBroadcastPlaybacksStore.getCurrent()?.pause();
 

src/components/structures/FilePanel.tsx

@@ -273,7 +273,9 @@ class FilePanel extends React.Component<IProps, IState> {
                         withoutScrollContainer
                         ref={this.card}
                     >
-                        <Measured sensor={this.card.current} onMeasurement={this.onMeasurement} />
+                        {this.card.current && (
+                            <Measured sensor={this.card.current} onMeasurement={this.onMeasurement} />
+                        )}
                         <SearchWarning isRoomEncrypted={isRoomEncrypted} kind={WarningKind.Files} />
                         <TimelinePanel
                             manageReadReceipts={false}

src/components/structures/LeftPanel.tsx

@@ -153,6 +153,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
     }
 
     private doStickyHeaders(list: HTMLDivElement): void {
+        if (!list.parentElement) return;
         const topEdge = list.scrollTop;
         const bottomEdge = list.offsetHeight + list.scrollTop;
         const sublists = list.querySelectorAll<HTMLDivElement>(".mx_RoomSublist:not(.mx_RoomSublist_hidden)");

src/components/structures/LegacyCallEventGrouper.ts

@@ -123,8 +123,8 @@ export default class LegacyCallEventGrouper extends EventEmitter {
     }
 
     public get duration(): number | null {
-        if (!this.hangup || !this.selectAnswer) return null;
+        if (!this.hangup?.getDate() || !this.selectAnswer?.getDate()) return null;
-        return this.hangup.getDate().getTime() - this.selectAnswer.getDate().getTime();
+        return this.hangup.getDate()!.getTime() - this.selectAnswer.getDate()!.getTime();
     }
 
     /**

src/components/structures/MatrixChat.tsx

@@ -169,7 +169,7 @@ interface IProps {
     // the initial queryParams extracted from the hash-fragment of the URI
     startingFragmentQueryParams?: QueryDict;
     // called when we have completed a token login
-    onTokenLoginCompleted?: () => void;
+    onTokenLoginCompleted: () => void;
     // Represents the screen to display as a result of parsing the initial window.location
     initialScreenAfterLogin?: IScreen;
     // displayname, if any, to set on the device when logging in/registering.
@@ -1200,7 +1200,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 // We have to manually update the room list because the forgotten room will not
                 // be notified to us, therefore the room list will have no other way of knowing
                 // the room is forgotten.
-                RoomListStore.instance.manualRoomUpdate(room, RoomUpdateCause.RoomRemoved);
+                if (room) RoomListStore.instance.manualRoomUpdate(room, RoomUpdateCause.RoomRemoved);
             })
             .catch((err) => {
                 const errCode = err.errcode || _td("unknown error code");
@@ -2124,7 +2124,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                     onForgotPasswordClick={showPasswordReset ? this.onForgotPasswordClick : undefined}
                     onServerConfigChange={this.onServerConfigChange}
                     fragmentAfterLogin={fragmentAfterLogin}
-                    defaultUsername={this.props.startingFragmentQueryParams.defaultUsername as string}
+                    defaultUsername={this.props.startingFragmentQueryParams?.defaultUsername as string | undefined}
                     {...this.getServerProperties()}
                 />
             );

src/components/structures/MessagePanel.tsx

@@ -24,6 +24,7 @@ import { logger } from "matrix-js-sdk/src/logger";
 import { RoomStateEvent } from "matrix-js-sdk/src/models/room-state";
 import { M_BEACON_INFO } from "matrix-js-sdk/src/@types/beacon";
 import { isSupportedReceiptType } from "matrix-js-sdk/src/utils";
+import { Optional } from "matrix-events-sdk";
 
 import shouldHideEvent from "../../shouldHideEvent";
 import { wantsDateSeparator } from "../../DateUtils";
@@ -436,10 +437,8 @@ export default class MessagePanel extends React.Component<IProps, IState> {
      * node (specifically, the bottom of it) will be positioned. If omitted, it
      * defaults to 0.
      */
-    public scrollToEvent(eventId: string, pixelOffset: number, offsetBase: number): void {
+    public scrollToEvent(eventId: string, pixelOffset?: number, offsetBase?: number): void {
-        if (this.scrollPanel.current) {
+        this.scrollPanel.current?.scrollToToken(eventId, pixelOffset, offsetBase);
-            this.scrollPanel.current.scrollToToken(eventId, pixelOffset, offsetBase);
-        }
     }
 
     public scrollToEventIfNeeded(eventId: string): void {
@@ -590,16 +589,16 @@ export default class MessagePanel extends React.Component<IProps, IState> {
         return { nextEventAndShouldShow, nextTile };
     }
 
-    private get pendingEditItem(): string | undefined {
+    private get pendingEditItem(): string | null {
         if (!this.props.room) {
-            return undefined;
+            return null;
         }
 
         try {
             return localStorage.getItem(editorRoomKey(this.props.room.roomId, this.context.timelineRenderingType));
         } catch (err) {
             logger.error(err);
-            return undefined;
+            return null;
         }
     }
 
@@ -815,7 +814,7 @@ export default class MessagePanel extends React.Component<IProps, IState> {
         return ret;
     }
 
-    public wantsDateSeparator(prevEvent: MatrixEvent | null, nextEventDate: Date): boolean {
+    public wantsDateSeparator(prevEvent: MatrixEvent | null, nextEventDate: Optional<Date>): boolean {
         if (this.context.timelineRenderingType === TimelineRenderingType.ThreadsList) {
             return false;
         }
@@ -1174,7 +1173,7 @@ class CreationGrouper extends BaseGrouper {
             const ts = createEvent.event.getTs();
             ret.push(
                 <li key={ts + "~"}>
-                    <DateSeparator roomId={createEvent.event.getRoomId()} ts={ts} />
+                    <DateSeparator roomId={createEvent.event.getRoomId()!} ts={ts} />
                 </li>,
             );
         }
@@ -1326,7 +1325,7 @@ class MainGrouper extends BaseGrouper {
             const ts = this.events[0].getTs();
             ret.push(
                 <li key={ts + "~"}>
-                    <DateSeparator roomId={this.events[0].getRoomId()} ts={ts} />
+                    <DateSeparator roomId={this.events[0].getRoomId()!} ts={ts} />
                 </li>,
             );
         }

src/components/structures/PipContainer.tsx

@@ -71,8 +71,8 @@ interface IState {
     secondaryCall: MatrixCall;
 
     // widget candidate to be displayed in the pip view.
-    persistentWidgetId: string;
+    persistentWidgetId: string | null;
-    persistentRoomId: string;
+    persistentRoomId: string | null;
     showWidgetInPip: boolean;
 }
 
@@ -225,7 +225,7 @@ class PipContainerInner extends React.Component<IProps, IState> {
         if (callRoomId ?? this.state.persistentRoomId) {
             dis.dispatch<ViewRoomPayload>({
                 action: Action.ViewRoom,
-                room_id: callRoomId ?? this.state.persistentRoomId,
+                room_id: callRoomId ?? this.state.persistentRoomId ?? undefined,
                 metricsTrigger: "WebFloatingCallWindow",
             });
         }
@@ -318,7 +318,7 @@ class PipContainerInner extends React.Component<IProps, IState> {
             pipContent.push(({ onStartMoving }) => (
                 <WidgetPip
                     widgetId={this.state.persistentWidgetId}
-                    room={MatrixClientPeg.get().getRoom(this.state.persistentRoomId)!}
+                    room={MatrixClientPeg.get().getRoom(this.state.persistentRoomId ?? undefined)!}
                     viewingRoom={this.state.viewedRoomId === this.state.persistentRoomId}
                     onStartMoving={onStartMoving}
                     movePersistedElement={this.props.movePersistedElement}

src/components/structures/RightPanel.tsx

@@ -218,36 +218,40 @@ export default class RightPanel extends React.Component<IProps, IState> {
                 }
                 break;
             case RightPanelPhases.Timeline:
-                card = (
+                if (this.props.room) {
-                    <TimelineCard
+                    card = (
-                        classNames="mx_ThreadPanel mx_TimelineCard"
+                        <TimelineCard
-                        room={this.props.room}
+                            classNames="mx_ThreadPanel mx_TimelineCard"
-                        timelineSet={this.props.room.getUnfilteredTimelineSet()}
+                            room={this.props.room}
-                        resizeNotifier={this.props.resizeNotifier}
+                            timelineSet={this.props.room.getUnfilteredTimelineSet()}
-                        onClose={this.onClose}
+                            resizeNotifier={this.props.resizeNotifier}
-                        permalinkCreator={this.props.permalinkCreator}
+                            onClose={this.onClose}
-                        e2eStatus={this.props.e2eStatus}
+                            permalinkCreator={this.props.permalinkCreator}
-                    />
+                            e2eStatus={this.props.e2eStatus}
-                );
+                        />
+                    );
+                }
                 break;
             case RightPanelPhases.FilePanel:
                 card = <FilePanel roomId={roomId} resizeNotifier={this.props.resizeNotifier} onClose={this.onClose} />;
                 break;
 
             case RightPanelPhases.ThreadView:
-                card = (
+                if (this.props.room) {
-                    <ThreadView
+                    card = (
-                        room={this.props.room}
+                        <ThreadView
-                        resizeNotifier={this.props.resizeNotifier}
+                            room={this.props.room}
-                        onClose={this.onClose}
+                            resizeNotifier={this.props.resizeNotifier}
-                        mxEvent={cardState?.threadHeadEvent}
+                            onClose={this.onClose}
-                        initialEvent={cardState?.initialEvent}
+                            mxEvent={cardState?.threadHeadEvent}
-                        isInitialEventHighlighted={cardState?.isInitialEventHighlighted}
+                            initialEvent={cardState?.initialEvent}
-                        initialEventScrollIntoView={cardState?.initialEventScrollIntoView}
+                            isInitialEventHighlighted={cardState?.isInitialEventHighlighted}
-                        permalinkCreator={this.props.permalinkCreator}
+                            initialEventScrollIntoView={cardState?.initialEventScrollIntoView}
-                        e2eStatus={this.props.e2eStatus}
+                            permalinkCreator={this.props.permalinkCreator}
-                    />
+                            e2eStatus={this.props.e2eStatus}
-                );
+                        />
+                    );
+                }
                 break;
 
             case RightPanelPhases.ThreadPanel:
@@ -262,18 +266,22 @@ export default class RightPanel extends React.Component<IProps, IState> {
                 break;
 
             case RightPanelPhases.RoomSummary:
-                card = (
+                if (this.props.room) {
-                    <RoomSummaryCard
+                    card = (
-                        room={this.props.room}
+                        <RoomSummaryCard
-                        onClose={this.onClose}
+                            room={this.props.room}
-                        // whenever RightPanel is passed a room it is passed a permalinkcreator
+                            onClose={this.onClose}
-                        permalinkCreator={this.props.permalinkCreator!}
+                            // whenever RightPanel is passed a room it is passed a permalinkcreator
-                    />
+                            permalinkCreator={this.props.permalinkCreator!}
-                );
+                        />
+                    );
+                }
                 break;
 
             case RightPanelPhases.Widget:
-                card = <WidgetCard room={this.props.room} widgetId={cardState?.widgetId} onClose={this.onClose} />;
+                if (this.props.room) {
+                    card = <WidgetCard room={this.props.room} widgetId={cardState?.widgetId} onClose={this.onClose} />;
+                }
                 break;
         }
 

src/components/structures/RoomView.tsx

@@ -654,7 +654,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
             // and the root event.
             // The rest will be lost for now, until the aggregation API on the server
             // becomes available to fetch a whole thread
-            if (!initialEvent && this.context.client) {
+            if (!initialEvent && this.context.client && roomId) {
                 initialEvent = (await fetchInitialEvent(this.context.client, roomId, initialEventId)) ?? undefined;
             }
 
@@ -741,7 +741,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
 
             // If an event ID wasn't specified, default to the one saved for this room
             // in the scroll state store. Assume initialEventPixelOffset should be set.
-            if (!newState.initialEventId) {
+            if (!newState.initialEventId && newState.roomId) {
                 const roomScrollState = RoomScrollStateStore.getScrollState(newState.roomId);
                 if (roomScrollState) {
                     newState.initialEventId = roomScrollState.focussedEvent;
@@ -770,7 +770,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         // callback because this would prevent the setStates from being batched,
         // ie. cause it to render RoomView twice rather than the once that is necessary.
         if (initial) {
-            this.setupRoom(newState.room, newState.roomId, newState.joining, newState.shouldPeek);
+            this.setupRoom(newState.room, newState.roomId, !!newState.joining, !!newState.shouldPeek);
         }
     };
 
@@ -794,13 +794,13 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.setState({ activeCall });
     };
 
-    private getRoomId = (): string => {
+    private getRoomId = (): string | undefined => {
         // According to `onRoomViewStoreUpdate`, `state.roomId` can be null
         // if we have a room alias we haven't resolved yet. To work around this,
         // first we'll try the room object if it's there, and then fallback to
         // the bare room ID. (We may want to update `state.roomId` after
         // resolving aliases, so we could always trust it.)
-        return this.state.room ? this.state.room.roomId : this.state.roomId;
+        return this.state.room?.roomId ?? this.state.roomId;
     };
 
     private getPermalinkCreatorForRoom(room: Room): RoomPermalinkCreator {
@@ -1008,7 +1008,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
             SettingsStore.unwatchSetting(watcher);
         }
 
-        if (this.viewsLocalRoom) {
+        if (this.viewsLocalRoom && this.state.room) {
             // clean up if this was a local room
             this.context.client?.store.removeRoom(this.state.room.roomId);
         }
@@ -1188,16 +1188,16 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
     };
 
     private onLocalRoomEvent(roomId: string): void {
-        if (roomId !== this.state.room.roomId) return;
+        if (!this.context.client || !this.state.room || roomId !== this.state.room.roomId) return;
         createRoomFromLocalRoom(this.context.client, this.state.room as LocalRoom);
     }
 
     private onRoomTimeline = (
         ev: MatrixEvent,
         room: Room | undefined,
-        toStartOfTimeline: boolean,
+        toStartOfTimeline: boolean | undefined,
         removed: boolean,
-        data?: IRoomTimelineData,
+        data: IRoomTimelineData,
     ): void => {
         if (this.unmounted) return;
 
@@ -1249,6 +1249,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
     };
 
     private handleEffects = (ev: MatrixEvent): void => {
+        if (!this.state.room) return;
         const notifState = this.context.roomNotificationStateStore.getRoomState(this.state.room);
         if (!notifState.isUnread) return;
 
@@ -1362,7 +1363,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
 
     private updatePreviewUrlVisibility({ roomId }: Room): void {
         // URL Previews in E2EE rooms can be a privacy leak so use a different setting which is per-room explicit
-        const key = this.context.client.isRoomEncrypted(roomId) ? "urlPreviewsEnabled_e2ee" : "urlPreviewsEnabled";
+        const key = this.context.client?.isRoomEncrypted(roomId) ? "urlPreviewsEnabled_e2ee" : "urlPreviewsEnabled";
         this.setState({
             showUrlPreview: SettingsStore.getValue(key, roomId),
         });
@@ -1661,7 +1662,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         this.setState({
             rejecting: true,
         });
-        this.context.client.leave(this.state.roomId).then(
+        this.context.client?.leave(this.state.roomId).then(
             () => {
                 dis.dispatch({ action: Action.ViewHomePage });
                 this.setState({
@@ -1691,13 +1692,13 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
         });
 
         try {
-            const myMember = this.state.room.getMember(this.context.client.getUserId());
+            const myMember = this.state.room!.getMember(this.context.client!.getSafeUserId());
-            const inviteEvent = myMember.events.member;
+            const inviteEvent = myMember!.events.member;
-            const ignoredUsers = this.context.client.getIgnoredUsers();
+            const ignoredUsers = this.context.client!.getIgnoredUsers();
-            ignoredUsers.push(inviteEvent.getSender()); // de-duped internally in the js-sdk
+            ignoredUsers.push(inviteEvent!.getSender()!); // de-duped internally in the js-sdk
-            await this.context.client.setIgnoredUsers(ignoredUsers);
+            await this.context.client!.setIgnoredUsers(ignoredUsers);
 
-            await this.context.client.leave(this.state.roomId);
+            await this.context.client!.leave(this.state.roomId!);
             dis.dispatch({ action: Action.ViewHomePage });
             this.setState({
                 rejecting: false,

src/components/structures/ScrollPanel.tsx

@@ -382,13 +382,12 @@ export default class ScrollPanel extends React.Component<IProps> {
         }
 
         const itemlist = this.itemlist.current;
-        const firstTile = itemlist && (itemlist.firstElementChild as HTMLElement);
+        const firstTile = itemlist?.firstElementChild as HTMLElement | undefined;
-        const contentTop = firstTile && firstTile.offsetTop;
         const fillPromises: Promise<void>[] = [];
 
         // if scrollTop gets to 1 screen from the top of the first tile,
         // try backward filling
-        if (!firstTile || sn.scrollTop - contentTop < sn.clientHeight) {
+        if (!firstTile || sn.scrollTop - firstTile.offsetTop < sn.clientHeight) {
             // need to back-fill
             fillPromises.push(this.maybeFill(depth, true));
         }
@@ -424,7 +423,7 @@ export default class ScrollPanel extends React.Component<IProps> {
     // check if unfilling is possible and send an unfill request if necessary
     private checkUnfillState(backwards: boolean): void {
         let excessHeight = this.getExcessHeight(backwards);
-        if (excessHeight <= 0) {
+        if (excessHeight <= 0 || !this.itemlist.current) {
             return;
         }
 
@@ -617,10 +616,7 @@ export default class ScrollPanel extends React.Component<IProps> {
      * node (specifically, the bottom of it) will be positioned. If omitted, it
      * defaults to 0.
      */
-    public scrollToToken = (scrollToken: string, pixelOffset: number, offsetBase: number): void => {
+    public scrollToToken = (scrollToken: string, pixelOffset = 0, offsetBase = 0): void => {
-        pixelOffset = pixelOffset || 0;
-        offsetBase = offsetBase || 0;
-
         // set the trackedScrollToken, so we can get the node through getTrackedNode
         this.scrollState = {
             stuckAtBottom: false,
@@ -652,6 +648,7 @@ export default class ScrollPanel extends React.Component<IProps> {
         const viewportBottom = scrollNode.scrollHeight - (scrollNode.scrollTop + scrollNode.clientHeight);
 
         const itemlist = this.itemlist.current;
+        if (!itemlist) return;
         const messages = itemlist.children;
         let node: HTMLElement | null = null;
 
@@ -705,7 +702,7 @@ export default class ScrollPanel extends React.Component<IProps> {
                 this.bottomGrowth += bottomDiff;
                 scrollState.bottomOffset = newBottomOffset;
                 const newHeight = `${this.getListHeight()}px`;
-                if (itemlist.style.height !== newHeight) {
+                if (itemlist && itemlist.style.height !== newHeight) {
                     itemlist.style.height = newHeight;
                 }
                 debuglog("balancing height because messages below viewport grew by", bottomDiff);
@@ -755,7 +752,7 @@ export default class ScrollPanel extends React.Component<IProps> {
 
         const scrollState = this.scrollState;
         if (scrollState.stuckAtBottom) {
-            if (itemlist.style.height !== newHeight) {
+            if (itemlist && itemlist.style.height !== newHeight) {
                 itemlist.style.height = newHeight;
             }
             if (sn.scrollTop !== sn.scrollHeight) {
@@ -770,7 +767,7 @@ export default class ScrollPanel extends React.Component<IProps> {
             // the currently filled piece of the timeline
             if (trackedNode) {
                 const oldTop = trackedNode.offsetTop;
-                if (itemlist.style.height !== newHeight) {
+                if (itemlist && itemlist.style.height !== newHeight) {
                     itemlist.style.height = newHeight;
                 }
                 const newTop = trackedNode.offsetTop;
@@ -823,9 +820,9 @@ export default class ScrollPanel extends React.Component<IProps> {
 
     private getMessagesHeight(): number {
         const itemlist = this.itemlist.current;
-        const lastNode = itemlist.lastElementChild as HTMLElement;
+        const lastNode = itemlist?.lastElementChild as HTMLElement;
         const lastNodeBottom = lastNode ? lastNode.offsetTop + lastNode.clientHeight : 0;
-        const firstNodeTop = itemlist.firstElementChild ? (itemlist.firstElementChild as HTMLElement).offsetTop : 0;
+        const firstNodeTop = (itemlist?.firstElementChild as HTMLElement)?.offsetTop ?? 0;
         // 18 is itemlist padding
         return lastNodeBottom - firstNodeTop + 18 * 2;
     }
@@ -865,8 +862,8 @@ export default class ScrollPanel extends React.Component<IProps> {
     */
     public preventShrinking = (): void => {
         const messageList = this.itemlist.current;
-        const tiles = messageList && messageList.children;
+        const tiles = messageList?.children;
-        if (!messageList) {
+        if (!tiles) {
             return;
         }
         let lastTileNode;

src/components/structures/TimelinePanel.tsx

@@ -777,7 +777,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         }
     };
 
-    public canResetTimeline = (): boolean => this.messagePanel?.current?.isAtBottom();
+    public canResetTimeline = (): boolean => this.messagePanel?.current?.isAtBottom() === true;
 
     private onRoomRedaction = (ev: MatrixEvent, room: Room): void => {
         if (this.unmounted) return;
@@ -1044,7 +1044,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
             const sendRRs = SettingsStore.getValue("sendReadReceipts", roomId);
 
             debuglog(
-                `Sending Read Markers for ${this.props.timelineSet.room.roomId}: `,
+                `Sending Read Markers for ${roomId}: `,
                 `rm=${this.state.readMarkerEventId} `,
                 `rr=${sendRRs ? lastReadEvent?.getId() : null} `,
                 `prr=${lastReadEvent?.getId()}`,
@@ -1092,7 +1092,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
                 // we only do this if we're right at the end, because we're just assuming
                 // that sending an RR for the latest message will set our notif counter
                 // to zero: it may not do this if we send an RR for somewhere before the end.
-                if (this.isAtEndOfLiveTimeline()) {
+                if (this.isAtEndOfLiveTimeline() && this.props.timelineSet.room) {
                     this.props.timelineSet.room.setUnreadNotificationCount(NotificationCountType.Total, 0);
                     this.props.timelineSet.room.setUnreadNotificationCount(NotificationCountType.Highlight, 0);
                     dis.dispatch({

src/components/views/rooms/MessageComposerFormatBar.tsx

@@ -99,7 +99,7 @@ export default class MessageComposerFormatBar extends React.PureComponent<IProps
     }
 
     public showAt(selectionRect: DOMRect): void {
-        if (!this.formatBarRef.current) return;
+        if (!this.formatBarRef.current?.parentElement) return;
 
         this.setState({ visible: true });
         const parentRect = this.formatBarRef.current.parentElement.getBoundingClientRect();

src/components/views/rooms/RoomPreviewBar.tsx

@@ -216,7 +216,7 @@ export default class RoomPreviewBar extends React.Component<IProps, IState> {
             return {};
         }
         const kickerMember = this.props.room?.currentState.getMember(myMember.events.member.getSender());
-        const memberName = kickerMember ? kickerMember.name : myMember.events.member.getSender();
+        const memberName = kickerMember?.name ?? myMember.events.member?.getSender();
         const reason = myMember.events.member?.getContent().reason;
         return { memberName, reason };
     }

src/components/views/rooms/RoomSublist.tsx

@@ -433,9 +433,11 @@ export default class RoomSublist extends React.Component<IProps, IState> {
     };
 
     private onHeaderClick = (): void => {
-        const possibleSticky = this.headerButton.current.parentElement;
+        const possibleSticky = this.headerButton.current?.parentElement;
-        const sublist = possibleSticky.parentElement.parentElement;
+        const sublist = possibleSticky?.parentElement?.parentElement;
-        const list = sublist.parentElement.parentElement;
+        const list = sublist?.parentElement?.parentElement;
+        if (!possibleSticky || !list) return;
+
         // the scrollTop is capped at the height of the header in LeftPanel, the top header is always sticky
         const listScrollTop = Math.round(list.scrollTop);
         const isAtTop = listScrollTop <= Math.round(HEADER_HEIGHT);

src/components/views/rooms/WhoIsTypingTile.tsx

@@ -91,7 +91,7 @@ export default class WhoIsTypingTile extends React.Component<IProps, IState> {
 
     private onRoomTimeline = (event: MatrixEvent, room?: Room): void => {
         if (room?.roomId === this.props.room.roomId) {
-            const userId = event.getSender();
+            const userId = event.getSender()!;
             // remove user from usersTyping
             const usersTyping = this.state.usersTyping.filter((m) => m.userId !== userId);
             if (usersTyping.length !== this.state.usersTyping.length) {
@@ -200,14 +200,15 @@ export default class WhoIsTypingTile extends React.Component<IProps, IState> {
     }
 
     public render(): React.ReactNode {
-        let usersTyping = this.state.usersTyping;
+        const usersTyping = this.state.usersTyping;
-        const stoppedUsersOnTimer = Object.keys(this.state.delayedStopTypingTimers).map((userId) =>
-            this.props.room.getMember(userId),
-        );
         // append the users that have been reported not typing anymore
         // but have a timeout timer running so they can disappear
         // when a message comes in
-        usersTyping = usersTyping.concat(stoppedUsersOnTimer);
+        for (const userId in this.state.delayedStopTypingTimers) {
+            const member = this.props.room.getMember(userId);
+            if (member) usersTyping.push(member);
+        }
+
         // sort them so the typing members don't change order when
         // moved to delayedStopTypingTimers
         usersTyping.sort((a, b) => compare(a.name, b.name));