Simplify null checks to fix IDE0031

[akoeplinger]

There's a Roslyn bug where the suggestion severity for dotnet_style_null_propagation in .editorconfig incorrectly overrides the IDE0031 warning severity set in eng/CodeAnalysis.src.globalconfig on some machines only (root cause is currently being investigated in dotnet/roslyn#80301).

This causes build breaks on machines where this doesn't happen and the IDE0031 warning severity is active (because of warnings-as-errors).

This PR fixes all the instances of IDE0031 that got hidden in the codebase.

Fixes #119391

[Copilot]

Pull Request Overview

This PR modernizes code by replacing an explicit null check with the null-coalescing operator in the LocalDataFlowState.cs file. The change simplifies the conditional assignment pattern by using the more concise ?. operator.

• Replaces if (Exception != null) check with null-conditional operator Exception?.

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[filipnavara]

I don't think this is the only affected place. It would make sense to flip suggestion to warning in
.editorconfig and then run the whole CI with consistent application of the rules.

[akoeplinger]

Yeah. I wanted to just fix this first since we see it on internal official builds.

[filipnavara]

Yeah. I wanted to just fix this first since we see it on internal official builds.

I did that locally and immediately run into error in a different file... hence my suggestion.

[akoeplinger]

ah ok

[filipnavara]

/Users/filipnavara/Projects/runtime/src/tools/illink/src/linker/Linker/DynamicDependency.cs(108,13): error IDE0031: Null check can be simplified (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0031) [/Users/filipnavara/Projects/runtime/src/tools/illink/src/linker/Mono.Linker.csproj]

[akoeplinger]

yeah. there's also a lot more in corelib

[sbomer]

The fix probably needs to be backported too (it started showing up in #119017 (comment) which went into .NET 10). If this needs to be unblocked before fixing all instances of the error we could also add it to NoWarn temporarily.

[akoeplinger]

I think for 10.0 we could probably just turn IDE0031 into suggestion in eng/CodeAnalysis.src.globalconfig

[akoeplinger]

Opened #119755 to "backport" this to 10.0