From 9e7c25d95161300de8a44f3065865d12b2311a22 Mon Sep 17 00:00:00 2001
From: Kalai <101443484+likalight@users.noreply.github.com>
Date: Mon, 24 Aug 2026 09:09:41 +0800
Subject: [PATCH] fix: keep content: null on an assistant tool-call turn
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`cleanup_none_field_in_message` dropped every key whose value was None,
so an assistant message carrying `tool_calls` lost its `content` key
entirely. That is the shape the OpenAI spec prescribes for a tool-call-only
turn, and providers that require the key to be present reject the request.

The helper's purpose, per its own docstring, is removing stray keys like
`{"function": None}` that trip provider validation — not `content`. Exempt
`content` when the assistant message carries `tool_calls` or a legacy
`function_call`; everything else still gets stripped, including a None
`content` on an assistant message with neither.

Reproduces with a plain `litellm.completion()` call, no proxy and no
credentials, via the intercept in the issue.

Fixes #37711

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 litellm/utils.py                              | 10 ++-
 .../test_cleanup_none_field_in_message.py     | 68 +++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 tests/test_litellm/test_cleanup_none_field_in_message.py

diff --git a/litellm/utils.py b/litellm/utils.py
index e5ce7157e77..3e17f57f7d5 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -7702,9 +7702,17 @@ def cleanup_none_field_in_message(message: AllMessageValues):
     Cleans up the message by removing the none field.
 
     remove None fields in the message - e.g. {"function": None} - some providers raise validation errors
+
+    `content` is exempt on an assistant tool-call turn. The OpenAI spec
+    prescribes `content: null` for an assistant message that only calls tools,
+    and providers that require the key to be present reject the request when it
+    is dropped entirely.
     """
     new_message: Final = message.copy()
-    return {k: v for k, v in new_message.items() if v is not None}
+    keeps_null_content: Final = message.get("role") == "assistant" and bool(
+        message.get("tool_calls") or message.get("function_call")
+    )
+    return {k: v for k, v in new_message.items() if v is not None or (k == "content" and keeps_null_content)}
 
 
 def validate_chat_completion_user_messages(messages: list[AllMessageValues]):
diff --git a/tests/test_litellm/test_cleanup_none_field_in_message.py b/tests/test_litellm/test_cleanup_none_field_in_message.py
new file mode 100644
index 00000000000..424c39e0024
--- /dev/null
+++ b/tests/test_litellm/test_cleanup_none_field_in_message.py
@@ -0,0 +1,68 @@
+"""`content: null` is the OpenAI-prescribed shape for an assistant tool-call turn."""
+
+from litellm.utils import cleanup_none_field_in_message, validate_and_fix_openai_messages
+
+TOOL_CALLS = [{"id": "call_1", "type": "function", "function": {"name": "f", "arguments": "{}"}}]
+
+
+class TestCleanupNoneFieldInMessage:
+    def test_keeps_null_content_on_a_tool_call_turn(self):
+        cleaned = cleanup_none_field_in_message(
+            message={"role": "assistant", "content": None, "tool_calls": TOOL_CALLS}
+        )
+
+        assert "content" in cleaned
+        assert cleaned["content"] is None
+
+    def test_keeps_null_content_on_a_legacy_function_call_turn(self):
+        cleaned = cleanup_none_field_in_message(
+            message={
+                "role": "assistant",
+                "content": None,
+                "function_call": {"name": "f", "arguments": "{}"},
+            }
+        )
+
+        assert "content" in cleaned
+
+    def test_still_strips_other_none_fields_on_that_turn(self):
+        # The original purpose of the helper: providers reject e.g. {"function": None}.
+        cleaned = cleanup_none_field_in_message(
+            message={
+                "role": "assistant",
+                "content": None,
+                "tool_calls": TOOL_CALLS,
+                "function": None,
+                "name": None,
+            }
+        )
+
+        assert "function" not in cleaned
+        assert "name" not in cleaned
+        assert "content" in cleaned
+
+    def test_still_strips_none_content_without_tool_calls(self):
+        cleaned = cleanup_none_field_in_message(message={"role": "assistant", "content": None})
+
+        assert "content" not in cleaned
+
+    def test_user_message_is_unaffected(self):
+        cleaned = cleanup_none_field_in_message(message={"role": "user", "content": None, "name": None})
+
+        assert cleaned == {"role": "user"}
+
+
+class TestValidateAndFixOpenAIMessages:
+    def test_tool_call_turn_survives_the_full_validation_pass(self):
+        """End to end through the caller that strips the field."""
+        messages = [
+            {"role": "user", "content": "hi"},
+            {"role": "assistant", "content": None, "tool_calls": TOOL_CALLS},
+            {"role": "tool", "tool_call_id": "call_1", "content": "ok"},
+        ]
+
+        fixed = validate_and_fix_openai_messages(messages=messages)
+
+        assert "content" in fixed[1]
+        assert fixed[1]["content"] is None
+        assert fixed[1]["tool_calls"] == TOOL_CALLS