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Source generator crashes with TUNIT0999 (NullReferenceException) for [Arguments(null)] on a generic test method #7120
Description
Summary
[Arguments(null)] on a generic test method makes the source generator crash with TUNIT0999 (NullReferenceException). C# binds a bare null to the params object?[] parameter as a null array rather than as one null element, and the generator's type-argument inference does not handle a null argument array.
Repro
public class NullArgumentsGeneric
{
[Test]
[Arguments(null)]
public void Run<T>(T value) { }
}The build reports TUNIT0999 from the TUnit source generator with a NullReferenceException.
Expected
No generator crash. Either treat the row as a single null value (inferring object, which is what source-gen does for [Arguments((string?)null)]) or report a clear diagnostic explaining that T cannot be inferred.
Notes
Found while addressing review on #7094. Reflection-mode behaviour for the same row has not been checked.
Activity
thomhurst commentedon Oct 18, 2026
PR #7111 (commit 5034196) makes the generator's three type-inference helpers treat
[Arguments(null)]as inferring no type instead of crashing. It was found for[Arguments(null)]on a generic class. Check whether the generic method repro here is also fixed once #7111 merges.thomhurst commentedon Oct 18, 2026
Another shape that hits the same crash: an untyped
[Arguments(null)]method row on a generic class. Found while addressing review on #7112. The new test there uses[Arguments((string?)null)]to avoid it.#7112 is built on #7102, not #7111, so it doesn't have #7111's null-array handling yet. Once #7111 merges, check this shape as well as the generic-method repro above.
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