diff --git a/litellm/types/utils.py b/litellm/types/utils.py
index f2b161128..a63e34738 100644
--- a/litellm/types/utils.py
+++ b/litellm/types/utils.py
@@ -168,11 +168,13 @@ class Function(OpenAIObject):
 
     def __init__(
         self,
-        arguments: Union[Dict, str],
+        arguments: Optional[Union[Dict, str]],
         name: Optional[str] = None,
         **params,
     ):
-        if isinstance(arguments, Dict):
+        if arguments is None:
+            arguments = ""
+        elif isinstance(arguments, Dict):
             arguments = json.dumps(arguments)
         else:
             arguments = arguments