Factor out collaboration code (#2313)

Co-authored-by: Lipis <lipiridis@gmail.com>
Co-authored-by: dwelle <luzar.david@gmail.com>

src/data/restore.ts

@@ -173,7 +173,7 @@ const restoreAppState = (
 };
 
 export const restore = (
-  data: ImportedDataState,
+  data: ImportedDataState | null,
   /**
    * Local AppState (`this.state` or initial state from localStorage) so that we
    * don't overwrite local state with default values (when values not
@@ -183,7 +183,7 @@ export const restore = (
   localAppState: Partial<AppState> | null | undefined,
 ): DataState => {
   return {
-    elements: restoreElements(data.elements),
-    appState: restoreAppState(data.appState, localAppState || null),
+    elements: restoreElements(data?.elements),
+    appState: restoreAppState(data?.appState, localAppState || null),
   };
 };