.Net: Fix: Enhance Function Argument Validation to Prevent Null Argument Exceptions in Tool Calls.

[shethaadit]

Motivation and Context

1. Why is this change required?
This change is required to prevent null pointer exceptions caused by invalid or empty function argument updates, which could lead to system crashes or unexpected behavior during runtime.

2. What problem does it solve?
It addresses the issue where the FunctionArgumentsUpdate was not being properly validated, causing the Semantic Kernel to throw a System.ArgumentNullException. This update ensures proper validation of function arguments before processing.

3. What scenario does it contribute to?
It improves the stability and reliability of tool call functions, particularly when interacting with external services like OpenAI, ensuring that memory operations are only executed on valid and non-empty inputs.

This PR resolves #9212.

Description

• Enhanced the validation logic for FunctionArgumentsUpdate by adding a check for both null and empty states, ensuring that invalid data is filtered out before processing.
• Refined the tool call processing flow to handle complex argument updates more gracefully.
• Improved error handling within the TrackStreamingToolingUpdate method, preventing memory issues and system crashes when receiving argument updates from external APIs.
• The change introduces a more robust approach to managing function argument updates and ensures tool calls are stable even in edge cases involving empty inputs.

Unit Test Details

• Created unit tests to validate the TrackStreamingToolingUpdate method when handling null values in FunctionArgumentsUpdate, ensuring it behaves correctly under various scenarios.
• Added a regression test to ensure that if the null check is removed in future changes, the test case will fail, providing an extra layer of protection against potential issues.

Contribution Checklist

• [Y] Code builds and passes tests.
• [Y] Unit tests added for edge case scenarios.
• [Y] Changes have been tested to ensure they do not break existing functionality.
• [N/A] Documentation updated where necessary.

[RogerBarreto]

@shethaadit Please agree and we can merge it.

[shethaadit]

@microsoft-github-policy-service agree company="Microsoft"

[shethaadit]

@microsoft-github-policy-service agree company="Microsoft"

[stephentoub]

For my edification, why is this additional clause required? Is it trying to be an optimization, or is it fixing an issue? Based on a cursory look at the code, for the condition that clause is guarding, I'd have expected arguments.Append(update.FunctionArgumentsUpdate.ToString()) to simply be the equivalent of arguments.Append(""), since BinaryData.ToString() just does Encoding.UTF8.GetString on the supplied bytes, and passing in an empty set of bytes will lead that to return an empty string.