[clang] [Clang] Fix crash on non-parameter NTTP arguments during partial ordering (PR #231599)

[Corentin Jabot via cfe-commits]

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@@ -5613,6 +5613,8 @@ bool Sema::CheckTemplateArgument(NamedDecl *Param, TemplateArgumentLoc &ArgLoc,
     //   parameter of type decltype(auto) ([temp.func.order]), the declaration
     //   is ill-formed.
     auto isUndeducedAuto = [](QualType T, bool DecltypeAuto) {
+      if (T.isNull())
+        return false;
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cor3ntin wrote:

And then we should not need that

https://github.com/llvm/llvm-project/pull/231599