fix(v2): handle consecutive None-content messages in merge_consecutive_messages

CHANGELOG.md

@@ -10,6 +10,7 @@ Versioning: [Semantic Versioning](https://semver.org/spec/v2.0.0.html)
 ## [Unreleased]
 
 ### Fixed
+- **v2 message handling**: `merge_consecutive_messages` no longer crashes with `AttributeError` when two consecutive same-role messages both have `content=None` (e.g. consecutive tool-call-only assistant turns in a replayed conversation history), affecting the OpenAI, Mistral, and Writer JSON-mode handlers.
 - **v2 message handling**: Preserve caller-owned message lists and nested content across request preparation and retries for OpenAI-compatible, Cohere, Mistral, OpenRouter, Writer, and xAI handlers. ([#2417](https://github.com/567-labs/instructor/issues/2417), [#2428](https://github.com/567-labs/instructor/issues/2428))
 - **v2 JSON extraction**: Prefer the final complete top-level JSON value in text responses and retain every JSON object when multiple objects arrive in one streaming chunk.
 - **v2 schemas**: Treat fields with Pydantic `default_factory` values as optional in generated OpenAI tool schemas.

instructor/v2/core/messages.py

@@ -83,6 +83,8 @@ def merge_consecutive_messages(messages: list[dict[str, Any]]) -> list[dict[str,
     for message in messages:
         role = message.get("role", "user")
         new_content = message.get("content", "")
+        if new_content is None:
+            new_content = ""
         if not flat_string and isinstance(new_content, str):
             new_content = [{"type": "text", "text": new_content}]
 

tests/processing/test_message_processing.py

@@ -88,6 +88,27 @@ def test_multiple_consecutive(self):
         assert result[2]["role"] == "user"
         assert "I need help" in result[2]["content"]
 
+    def test_consecutive_none_content(self):
+        """Consecutive same-role messages with content=None (e.g. tool-call-only
+        assistant turns) must not crash the merge."""
+        messages = [
+            {"role": "user", "content": "hi"},
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [{"id": "call_1"}],
+            },
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [{"id": "call_2"}],
+            },
+        ]
+        result = merge_consecutive_messages(messages)
+        assert len(result) == 2
+        assert result[0]["role"] == "user"
+        assert result[1]["role"] == "assistant"
+
 
 class TestGetMessageContent:
     """Test the get_message_content function."""