Strict fixes.

Author: clokep

Diff for: src/components/views/rooms/EditMessageComposer.tsx

@@ -85,7 +85,7 @@ export function attachDifferentialMentions(sender: string, editedContent: IConte
     const prevMentions = editedContent["org.matrix.msc3952.mentions"];
     const prevUserMentions = new Set();
     if (Array.isArray(prevMentions?.user_ids)) {
-        prevMentions.user_ids.forEach((userId) => prevUserMentions.add(userId));
+        prevMentions!.user_ids.forEach((userId) => prevUserMentions.add(userId));
     }
 
     // Generate the differential mentions: users who were not previously mentioned
@@ -150,8 +150,8 @@ export function createEditContent(model: EditorModel, editedEvent: MatrixEvent):
     // Build the mentions property for the *new* content (as if there was no edit).
     //
     // TODO If this is a reply we need to include all the users from it.
-    attachMentions(editedEvent.sender.userId, newContent, model, undefined);
-    const mentions = attachDifferentialMentions(editedEvent.sender.userId, editedEvent.getContent(), model);
+    attachMentions(editedEvent.sender!.userId, newContent, model, undefined);
+    const mentions = attachDifferentialMentions(editedEvent.sender!.userId, editedEvent.getContent(), model);
 
     return Object.assign(
         {

Diff for: src/components/views/rooms/SendMessageComposer.tsx

@@ -86,7 +86,7 @@ export function attachMentions(
     // If there's a reply, initialize the mentioned users as the sender of that
     // event + any mentioned users in that event.
     if (replyToEvent) {
-        userMentions.add(replyToEvent.sender.userId);
+        userMentions.add(replyToEvent.sender!.userId);
         // TODO What do we do if the prely event *doeesn't* have this property?
         // Try to fish out replies from the contents?
         const userIds = replyToEvent.getContent()["org.matrix.msc3952.mentions"]?.user_ids;
@@ -471,7 +471,7 @@ export class SendMessageComposer extends React.Component<ISendMessageComposerPro
             const { roomId } = this.props.room;
             if (!content) {
                 content = createMessageContent(
-                    this.props.mxClient.getUserId(),
+                    this.props.mxClient.getUserId()!,
                     model,
                     replyToEvent,
                     this.props.relation,