[Bugfix] Handle None parameters in Mistral function calls.

tests/tokenization/test_mistral_tokenizer.py

@@ -41,7 +41,40 @@
                 )
             ],
         ),
-    )],
+    ),
+     (
+         {
+             "messages":
+             [{
+                 "role": "user",
+                 "content": "What is the current local date and time?",
+             }],
+             "tools": [{
+                 "type": "function",
+                 "function": {
+                     "description": "Fetch the current local date and time.",
+                     "name": "get_current_time",
+                     "parameters": None,
+                 },
+             }],
+         },
+         ChatCompletionRequest(
+             messages=[
+                 UserMessage(
+                     content="What is the current local date and time?")
+             ],
+             tools=[
+                 Tool(
+                     type="function",
+                     function=Function(
+                         name="get_current_time",
+                         description="Fetch the current local date and time.",
+                         parameters={},
+                     ),
+                 )
+             ],
+         ),
+     )],
 )
 def test_make_mistral_chat_completion_request(openai_request,
                                               expected_mistral_request):

vllm/transformers_utils/tokenizers/mistral.py

@@ -164,7 +164,8 @@ def make_mistral_chat_completion_request(
                 tool["function"] for tool in tools
                 if tool["type"] == "function"
         ]:
-            function.setdefault("parameters", {})
+            if function.get("parameters") is None:
+                function["parameters"] = {}
 
     from mistral_common.protocol.instruct.request import ChatCompletionRequest
     return ChatCompletionRequest(messages=messages,