.Net: Bug: JsonReaderException when OpenAI ChatCompletion returns empty or invalid response in Semantic Kernel

[akshay-msft-09]

Describe the bug
When calling Kernel.InvokeAsync() with a prompt that uses an OpenAI Chat Completion service, the execution fails with:

System.Text.Json.JsonReaderException: The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true.  
   at System.Text.Json.JsonDocument.Parse(...)  
   at OpenAI.Chat.ChatCompletion.op_Explicit(ClientResult result)  
   at OpenAI.Chat.ChatClient.CompleteChatAsync(...)  
   at Microsoft.SemanticKernel.Connectors.OpenAI.ClientCore.RunRequestAsync[T](...)  

It appears that the Semantic Kernel connector is attempting to parse an empty or non‑JSON response from the model.

To Reproduce

• Create a Kernel instance with the OpenAI Chat Completion connector (IChatCompletionService).
• Pass in a prompt to KernelFunctionFromPrompt.InvokeAsync() that results in an empty or malformed API response.
• Observe that the SDK throws a JsonReaderException instead of handling the empty/malformed response gracefully.
• Expected behavior
• Semantic Kernel should handle empty or invalid JSON responses from the model gracefully — either by returning a clear error message or retrying — instead of throwing an unhandled exception.

Platform

Language: C#
Semantic Kernel Source: NuGet package (please specify exact version, e.g., 1.12.0)

    <PackageVersion Include="Microsoft.SemanticKernel" Version="1.65.0" />
    <PackageVersion Include="Microsoft.SemanticKernel.Abstractions" Version="1.33.0" />
    <PackageVersion Include="Microsoft.SemanticKernel.Agents.Abstractions" Version="1.45.0" />
    <PackageVersion Include="Microsoft.SemanticKernel.Agents.AzureAI" Version="1.66.0-preview" />
    <PackageVersion Include="Microsoft.SemanticKernel.Agents.Core" Version="1.45.0" />
    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.AI.OpenAI" Version="0.17.230704.3-preview" />
    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.AzureAISearch" Version="1.33.0-preview" />
    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.AzureOpenAI" Version="1.65.0" />
    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.Memory.AzureAISearch" Version="1.0.0-rc3" />
    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.OpenAI" Version="1.33.0" />
    <PackageVersion Include="Microsoft.SemanticKernel.Planners.Handlebars" Version="1.33.0-preview" />
    <PackageVersion Include="Microsoft.SemanticKernel.Plugins.Memory" Version="1.33.0-alpha" />

AI Model: OpenAI GPT‑4o‑mini (or whichever model you used) : GPT o3 mini (Behind Azure API Management)
Additional context
The issue appears to be triggered when the OpenAI service returns an unexpected payload (possibly empty). This could happen if:

• The request was malformed.
• The model returned no content due to filtering.
• There was an upstream network or API gateway issue.
• Suggest adding null/empty checks before parsing JSON in OpenAI.Chat.ChatCompletion.op_Explicit or in ClientCore.RunRequestAsync.