fix

lib/Persistent.ts

@@ -33,7 +33,7 @@ export abstract class Persistent implements Assignable, Serializable {
   }
 
   public to_object (): Record<string, PersistentType> {
-    return copy_object (this._data);
+    return copy_object (this._data) as Record<string, PersistentType>;
   }
 
   public serialize (formatted = false): string {