Improving C# Null Reference Exception Diagnostics: Adding Variable Names to Error Messages

[Liangjia0411]

When working with C# applications, one of the most common runtime errors is the NullReferenceException. While this exception correctly identifies that we're attempting to access a member on a null reference, it lacks critical context: which variable was null?

The standard exception message:

System.NullReferenceException: Object reference not set to an instance of an object.

provides minimal debugging information, especially in complex code paths or when multiple nullable references are involved.

Current Challenges

This limitation creates several issues:

• Increased debugging time in complex methods with multiple potential null sources
• Difficulty identifying the root cause in production environments where only logs are available
• Extra code needed for defensive programming to provide meaningful error messages

[huoyaoyuan]

This is impossible without debugger. Variable names (or even the original local variables) are totally nothing in compiled assembly. They only appear in debug symbol.

See #104703 and #3858.