Null guard space hierarchy (#7729)

Author: t3chguy

src/components/structures/SpaceHierarchy.tsx

@@ -475,7 +475,7 @@ const INITIAL_PAGE_SIZE = 20;
 
 export const useRoomHierarchy = (space: Room): {
     loading: boolean;
-    rooms: IHierarchyRoom[];
+    rooms?: IHierarchyRoom[];
     hierarchy: RoomHierarchy;
     error: Error;
     loadMore(pageSize?: number): Promise<void>;
@@ -716,7 +716,7 @@ const SpaceHierarchy = ({
     return <RovingTabIndexProvider onKeyDown={onKeyDown} handleHomeEnd handleUpDown>
         { ({ onKeyDownHandler }) => {
             let content: JSX.Element;
-            if (loading && !rooms.length) {
+            if (loading && !rooms?.length) {
                 content = <Spinner />;
             } else {
                 const hasPermissions = space?.getMyMembership() === "join" &&