Fix soft crash around unknown room pills (#9301)

* Fix soft crash around unknown room pills

* Add tests

* Fix types

src/editor/parts.ts

@@ -411,7 +411,7 @@ export class EmojiPart extends BasePart implements IBasePart {
 }
 
 class RoomPillPart extends PillPart {
-    constructor(resourceId: string, label: string, private room: Room) {
+    constructor(resourceId: string, label: string, private room?: Room) {
         super(resourceId, label);
     }
 
@@ -419,8 +419,8 @@ class RoomPillPart extends PillPart {
         let initialLetter = "";
         let avatarUrl = Avatar.avatarUrlForRoom(this.room, 16, 16, "crop");
         if (!avatarUrl) {
-            initialLetter = Avatar.getInitialLetter(this.room ? this.room.name : this.resourceId);
-            avatarUrl = Avatar.defaultAvatarUrlForString(this.room ? this.room.roomId : this.resourceId);
+            initialLetter = Avatar.getInitialLetter(this.room?.name || this.resourceId);
+            avatarUrl = Avatar.defaultAvatarUrlForString(this.room?.roomId ?? this.resourceId);
         }
         this.setAvatarVars(node, avatarUrl, initialLetter);
     }
@@ -430,7 +430,7 @@ class RoomPillPart extends PillPart {
     }
 
     protected get className() {
-        return "mx_Pill " + (this.room.isSpaceRoom() ? "mx_SpacePill" : "mx_RoomPill");
+        return "mx_Pill " + (this.room?.isSpaceRoom() ? "mx_SpacePill" : "mx_RoomPill");
     }
 }
 
@@ -610,7 +610,7 @@ export class PartCreator {
     }
 
     public roomPill(alias: string, roomId?: string): RoomPillPart {
-        let room;
+        let room: Room | undefined;
         if (roomId || alias[0] !== "#") {
             room = this.client.getRoom(roomId || alias);
         } else {

test/editor/parts-test.ts

@@ -15,6 +15,7 @@ limitations under the License.
 */
 
 import { EmojiPart, PlainPart } from "../../src/editor/parts";
+import { createPartCreator } from "./mock";
 
 describe("editor/parts", () => {
     describe("appendUntilRejected", () => {
@@ -32,4 +33,10 @@ describe("editor/parts", () => {
             expect(part.text).toEqual(femaleFacepalmEmoji);
         });
     });
+
+    it("should not explode on room pills for unknown rooms", () => {
+        const pc = createPartCreator();
+        const part = pc.roomPill("#room:server");
+        expect(() => part.toDOMNode()).not.toThrow();
+    });
 });