Error Detail Null Fields Ignored

Preflight Checklist

• I have installed the latest version of Power Query SDK.
• I have checked existing resources, including the common issues and the release notes.
• I have searched for similar issues.

Power Query SDK

v0.4.0

Regression From

No response

Platform

Windows

Architecture

x64

OS Version

No response

VSCode version

No response

PQSdkTool Path

No response

Bug Description

Null fields in an error's details are ignored when the error is reported.

Steps to Reproduce

1. Create a new connector project.
2. Replace the contents of the .test.pq with the following:

   error [Detail = [a = 123, b = null, c = 456]]
   

3. Evaluate the current file.

Actual Experience

Output contains the following:

"Error": {
            "Message": "Exception of type 'Microsoft.Data.Mashup.MashupValueException' was thrown.",
            "Details": {
                "Reason": "Expression.Error",
                "a": 123,
                "c": 456
            }
        }

Expected Experience

Details should also include field b.

Additional Context

No response

Start with the reported .test.pq reproduction and evaluate the current file to observe how the error details are rendered. Trace the error-reporting path that handles the Detail record, then verify that the output includes field b with a null value alongside fields a and c.