fix(api) - Defaults to {} when none metadata is supplied (#897)

* Fixes null metadata in cases where null metadata is explicitly trying to be inserted into the db by replacing it before db insert.

src/leapfrogai_api/data/crud_message.py

@@ -10,3 +10,9 @@ class CRUDMessage(CRUDBase[Message]):
 
     def __init__(self, db: AsyncClient):
         super().__init__(db=db, model=Message, table_name="message_objects")
+
+    async def create(self, object_: Message) -> Message | None:
+        if object_.metadata is None:
+            object_.metadata = {}
+
+        return await super().create(object_)