fix: Mistral "Object reference not set to an intance of object" #317
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Add comprehensive unit tests for MistralThinkingBehavior and Mistral provider to reproduce and verify issue #309 ("Mistral provider broken" with "Object reference not set to an instance of an object" error). Tests cover: - MistralThinkingBehavior with null/empty text in assistant messages - Thinking response extraction from JSON arrays - Edge cases with malformed JSON responses - ChatMessage and ChatResponse handling with null text - Mocked IChatClient scenarios simulating Mistral SDK behavior - Exact pattern used in CellmFunctions.cs line 317
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kaspermarstal
changed the title
ROOT CAUSE IDENTIFIED:
The bug is in Mistral.SDK v2.3.0's CompletionsEndpoint.ChatClient.cs
in the ProcessResponseContent method:
```csharp
foreach (var content in response.Choices)
{
if (content.Message.ToolCalls is not null) // BUG: No null check!
```
When the Mistral API returns a response where Choice.Message is null
(which can happen in edge cases), accessing content.Message.ToolCalls
throws NullReferenceException: "Object reference not set to an
instance of an object"
COMPARISON:
- Streaming code (CORRECT): choice.Delta?.ToolCalls (null-conditional)
- Non-streaming (BUG): content.Message.ToolCalls (no null check)
The tests simulate the exact JSON response that triggers the bug
by creating a response without a message field, which deserializes
to null.
FIX: The SDK should use content.Message?.ToolCalls instead.
- Add #pragma warning disable for intentional null dereference in bug reproduction test - Rename async method to use 'Async' suffix per naming conventions
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Add comprehensive unit tests for MistralThinkingBehavior and Mistral provider to reproduce and verify issue #309 ("Mistral provider broken" with "Object reference not set to an instance of an object" error).
Tests cover: