Handle missing predecessor

Author: andybalaam

src/components/views/messages/RoomCreate.tsx

@@ -63,7 +63,7 @@ export const RoomCreate: React.FC<IProps> = ({ mxEvent, timestamp }) => {
                 metricsViaKeyboard: e.type !== "click",
             });
         },
-        [predecessor.eventId, predecessor.roomId],
+        [predecessor?.eventId, predecessor?.roomId],
     );
 
     if (!roomContext.room || roomContext.room.roomId !== mxEvent.getRoomId()) {

test/components/views/messages/RoomCreate-test.tsx

@@ -72,7 +72,7 @@ describe("<RoomCreate />", () => {
         jest.spyOn(SettingsStore, "setValue").mockRestore();
     });
 
-    function renderRoomCreate() {
+    function renderRoomCreate(room: Room) {
         return render(
             <RoomContext.Provider value={getRoomContext(room, {})}>
                 <RoomCreate mxEvent={createEvent} />
@@ -81,20 +81,25 @@ describe("<RoomCreate />", () => {
     }
 
     it("Renders as expected", () => {
-        const roomCreate = renderRoomCreate();
+        const roomCreate = renderRoomCreate(room);
         expect(roomCreate.asFragment()).toMatchSnapshot();
     });
 
     it("Links to the old version of the room", () => {
-        renderRoomCreate();
+        renderRoomCreate(room);
         expect(screen.getByText("Click here to see older messages.")).toHaveAttribute(
             "href",
             "https://matrix.to/#/old_room_id/tombstone_event_id",
         );
     });
 
+    it("Shows an empty div if there is no predecessor", () => {
+        renderRoomCreate(roomNoPredecessors);
+        expect(screen.queryByText("Click here to see older messages.", { exact: false })).toBeNull();
+    });
+
     it("Opens the old room on click", async () => {
-        renderRoomCreate();
+        renderRoomCreate(room);
         const link = screen.getByText("Click here to see older messages.");
 
         await act(() => userEvent.click(link));