fix(parallel_request_limiter.py): handle metadata being none

litellm/main.py

@@ -3682,11 +3682,12 @@ async def ahealth_check(
                 response = {}  # args like remaining ratelimit etc.
         return response
     except Exception as e:
+        traceback.print_exc()
         if model not in litellm.model_cost and mode is None:
             raise Exception(
                 "Missing `mode`. Set the `mode` for the model - https://docs.litellm.ai/docs/proxy/health#embedding-models"
             )
-        return {"error": str(e)}
+        return {"error": f"{str(e)}"}
 
 
 ####### HELPER FUNCTIONS ################