{"record":{"id":"ec969ad7196cb763","repo":"microsoft/autogen","slug":"response-choices","errorCode":null,"errorMessage":"response.Choices","messagePattern":"response\\.Choices","errorType":"exception","errorClass":"ArgumentNullException","httpStatus":null,"severity":"error","filePath":"dotnet/src/AutoGen.Mistral/Middleware/MistralChatMessageConnector.cs","lineNumber":143,"sourceCode":"            else\n            {\n                return m switch\n                {\n                    TextMessage textMessage => ProcessTextMessage(textMessage, agent),\n                    ToolCallMessage toolCallMessage when (toolCallMessage.From is null || toolCallMessage.From == agent.Name) => ProcessToolCallMessage(toolCallMessage, agent),\n                    ToolCallResultMessage toolCallResultMessage => ProcessToolCallResultMessage(toolCallResultMessage, agent),\n                    AggregateMessage<ToolCallMessage, ToolCallResultMessage> aggregateMessage => ProcessFunctionCallMiddlewareMessage(aggregateMessage, agent), // message type support for functioncall middleware\n                    _ => [m],\n                };\n            }\n        });\n    }\n\n    private IMessage PostProcessMessage(ChatCompletionResponse response, IAgent from)\n    {\n        if (response.Choices is null)\n        {\n            throw new ArgumentNullException(\"response.Choices\");\n        }\n\n        if (response.Choices?.Count != 1)\n        {\n            throw new NotSupportedException(\"response.Choices.Count != 1\");\n        }\n\n        var choice = response.Choices[0];\n        var finishReason = choice.FinishReason ?? throw new ArgumentNullException(\"choice.FinishReason\");\n\n        if (finishReason == Choice.FinishReasonEnum.Stop || finishReason == Choice.FinishReasonEnum.Length)\n        {\n            return new TextMessage(Role.Assistant, choice.Message?.Content ?? throw new ArgumentNullException(\"choice.Message.Content\"), from: from.Name);\n        }\n        else if (finishReason == Choice.FinishReasonEnum.ToolCalls)\n        {\n            var functionContents = choice.Message?.ToolCalls ?? throw new ArgumentNullException(\"choice.Message.ToolCalls\");\n            var toolCalls = functionContents.Select(f => new ToolCall(f.Function.Name, f.Function.Arguments) { ToolCallId = f.Id }).ToList();","sourceCodeStart":125,"sourceCodeEnd":161,"githubUrl":"https://github.com/microsoft/autogen/blob/027ecf0a379bcc1d09956d46d12d44a3ad9cee14/dotnet/src/AutoGen.Mistral/Middleware/MistralChatMessageConnector.cs#L125-L161","documentation":"MistralChatMessageConnector.PostProcessMessage requires the ChatCompletionResponse to contain a Choices collection before it can map a choice to an AutoGen message; a null Choices (explicitly null in the payload, e.g. an error or malformed body) triggers ArgumentNullException.","triggerScenarios":"A Mistral chat-completion response whose JSON has \"choices\": null or omits it while deserializing to a non-null-but-default state — commonly the API returned an error object or an unexpected payload shape instead of a completion.","commonSituations":"Invalid API key / quota errors returned as JSON without choices; Mistral API schema changes; hitting a non-completion endpoint by misconfiguration; proxy returning a different error body.","solutions":["Check the HTTP status and raw body of the failing request (enable response logging) — a null Choices usually means an error payload, and the real cause (auth, quota) is in that body.","Verify the Mistral API key and account quota.","Confirm the model name is valid; invalid models can return error-shaped bodies.","Update AutoGen.Mistral / Mistral SDK if the schema drifted."],"exampleFix":null,"handlingStrategy":"validation","validationCode":"if (response.Choices is null)\n{\n    // inspect raw body: usually auth/quota error — do not proceed to the connector\n}","typeGuard":null,"tryCatchPattern":"try { var reply = await mistralAgent.SendAsync(msg); } catch (ArgumentNullException ex) when (ex.ParamName == \"response.Choices\") { /* check API key/quota/raw body */ }","preventionTips":["Enable HTTP logging to catch error-shaped bodies","Verify API key and quota before runs","Confirm model names are valid"],"tags":["mistral","response-parsing","null-argument","api-error"],"backgroundTag":null,"analyzedSha":"027ecf0a379bcc1d09956d46d12d44a3ad9cee14","analyzedAt":"2026-08-15T03:38:00.719Z","schemaVersion":2},"datasetVersion":"2026-08-15T17:31:12.345Z"}