tweaks for server using serialization

serializable.py

@@ -11,7 +11,7 @@ class Serializable:
         instance.deserialize_dict(data)
         return instance
 
-    def serialize(self, file) -> str:
+    def serialize(self, file=None) -> str:
         """Serializes the object and all nested Serializable objects to JSON."""
         def serialize_value(value: Any) -> Any:
             if isinstance(value, Serializable):
@@ -24,7 +24,9 @@ class Serializable:
                 return value
 
         attrs = {k: serialize_value(v) for k, v in self.__dict__.items() if not k.startswith('_')}
-        return json.dumps(attrs, file, ensure_ascii=False, indent=2)
+        if file:
+            json.dump(attrs, file, ensure_ascii=False, indent=2)
+        return json.dumps(attrs, ensure_ascii=False, indent=2)
 
     def serialize_dict(self) -> Dict[str, Any]:
         """Serializes the object to a dictionary (for nested serialization)."""