fix(genai-openai): fix for ChoiceBuffer crashes on streaming tool-call deltas with arguments=None. (open-telemetry#4350)

* wip: fix for none/null in function tool calls.

* polish: add changelog.

* wip: fixing lint and precommit.

* wip: converted class based tests.

* wip: fixing the precommit.

Author: eternalcuriouslearner

instrumentation-genai/opentelemetry-instrumentation-openai-v2/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Fix `ChoiceBuffer` crash on streaming tool-call deltas with `arguments=None`
+  ([#4350](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4350))
 - Fix `StreamWrapper` missing `.headers` and other attributes when using `with_raw_response` streaming
   ([#4113](https://github.com/open-telemetry/opentelemetry-python-contrib/issues/4113))
 - Add opt-in support for latest experimental semantic conventions (v1.37.0). Set

instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/patch.py

@@ -582,7 +582,8 @@ def __init__(self, index, tool_call_id, function_name):
         self.arguments = []
 
     def append_arguments(self, arguments):
-        self.arguments.append(arguments)
+        if arguments is not None:
+            self.arguments.append(arguments)
 
 
 class ChoiceBuffer:
@@ -601,13 +602,16 @@ def append_tool_call(self, tool_call):
         for _ in range(len(self.tool_calls_buffers), idx + 1):
             self.tool_calls_buffers.append(None)
 
+        function = tool_call.function
         if not self.tool_calls_buffers[idx]:
             self.tool_calls_buffers[idx] = ToolCallBuffer(
-                idx, tool_call.id, tool_call.function.name
+                idx,
+                tool_call.id,
+                function.name if function else None,
             )
-        self.tool_calls_buffers[idx].append_arguments(
-            tool_call.function.arguments
-        )
+
+        if function:
+            self.tool_calls_buffers[idx].append_arguments(function.arguments)
 
 
 class BaseStreamWrapper:

instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_choice_buffer.py

@@ -0,0 +1,182 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unit tests for ChoiceBuffer and ToolCallBuffer classes."""
+
+from openai.types.chat.chat_completion_chunk import (
+    ChoiceDeltaToolCall,
+    ChoiceDeltaToolCallFunction,
+)
+
+from opentelemetry.instrumentation.openai_v2.patch import (
+    ChoiceBuffer,
+    ToolCallBuffer,
+)
+
+
+def test_toolcallbuffer_append_arguments_with_string():
+    buf = ToolCallBuffer(0, "call_1", "get_weather")
+    buf.append_arguments('{"city":')
+    buf.append_arguments(' "NYC"}')
+    assert "".join(buf.arguments) == '{"city": "NYC"}'
+
+
+def test_toolcallbuffer_append_arguments_with_none_is_skipped():
+    """Regression test for issue #4344.
+
+    Some OpenAI-compatible providers (vLLM, TGI, etc.) send
+    arguments=None on tool-call delta chunks instead of arguments="".
+    This must not crash when joining the arguments list.
+    """
+    buf = ToolCallBuffer(0, "call_1", "get_weather")
+    buf.append_arguments(None)
+    buf.append_arguments('{"city": "NYC"}')
+    buf.append_arguments(None)
+    assert "".join(buf.arguments) == '{"city": "NYC"}'
+
+
+def test_toolcallbuffer_append_arguments_all_none():
+    buf = ToolCallBuffer(0, "call_1", "get_weather")
+    buf.append_arguments(None)
+    buf.append_arguments(None)
+    assert "".join(buf.arguments) == ""
+
+
+def test_toolcallbuffer_append_arguments_empty_string():
+    buf = ToolCallBuffer(0, "call_1", "get_weather")
+    buf.append_arguments("")
+    buf.append_arguments('{"city": "NYC"}')
+    assert "".join(buf.arguments) == '{"city": "NYC"}'
+
+
+def test_choicebuffer_append_tool_call_with_none_arguments():
+    """End-to-end regression test for issue #4344.
+
+    Simulates the exact scenario from the bug report where a provider
+    sends arguments=None on the first tool-call delta chunk.
+    """
+    buf = ChoiceBuffer(0)
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            id="call_1",
+            type="function",
+            function=ChoiceDeltaToolCallFunction(
+                name="get_weather", arguments=None
+            ),
+        )
+    )
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            function=ChoiceDeltaToolCallFunction(arguments='{"city": "NYC"}'),
+        )
+    )
+
+    # This must not raise TypeError
+    result = "".join(buf.tool_calls_buffers[0].arguments)
+    assert result == '{"city": "NYC"}'
+
+
+def test_choicebuffer_append_tool_call_normal_flow():
+    """Standard OpenAI flow where arguments="" on first delta."""
+    buf = ChoiceBuffer(0)
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            id="call_1",
+            type="function",
+            function=ChoiceDeltaToolCallFunction(
+                name="get_weather", arguments=""
+            ),
+        )
+    )
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            function=ChoiceDeltaToolCallFunction(arguments='{"city": "NYC"}'),
+        )
+    )
+
+    result = "".join(buf.tool_calls_buffers[0].arguments)
+    assert result == '{"city": "NYC"}'
+
+
+def test_choicebuffer_append_multiple_tool_calls_with_none_arguments():
+    """Multiple tool calls where some have arguments=None."""
+    buf = ChoiceBuffer(0)
+
+    # First tool call
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            id="call_1",
+            type="function",
+            function=ChoiceDeltaToolCallFunction(
+                name="get_weather", arguments=None
+            ),
+        )
+    )
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            function=ChoiceDeltaToolCallFunction(arguments='{"city": "NYC"}'),
+        )
+    )
+
+    # Second tool call
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=1,
+            id="call_2",
+            type="function",
+            function=ChoiceDeltaToolCallFunction(
+                name="get_time", arguments=None
+            ),
+        )
+    )
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=1,
+            function=ChoiceDeltaToolCallFunction(arguments='{"tz": "EST"}'),
+        )
+    )
+
+    assert "".join(buf.tool_calls_buffers[0].arguments) == '{"city": "NYC"}'
+    assert "".join(buf.tool_calls_buffers[1].arguments) == '{"tz": "EST"}'
+
+
+def test_choicebuffer_append_tool_call_with_none_function():
+    """Handle delta chunks where function is None."""
+    buf = ChoiceBuffer(0)
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            id="call_1",
+            type="function",
+            function=ChoiceDeltaToolCallFunction(
+                name="get_weather", arguments='{"city": "NYC"}'
+            ),
+        )
+    )
+    # Subsequent delta with function=None should not crash
+    buf.append_tool_call(
+        ChoiceDeltaToolCall(
+            index=0,
+            function=None,
+        )
+    )
+
+    result = "".join(buf.tool_calls_buffers[0].arguments)
+    assert result == '{"city": "NYC"}'