Make StringComparer.Create throw ArgumentNullException

[TylerBrinkley]

Throws proper exception.

@danmosemsft

[danmoseley]

thanks @TylerBrinkley

[danmoseley]

Oh, we forgot it is necessary to update https://github.com/dotnet/coreclr/blob/master/tests/CoreFX/CoreFX.issues.rsp to make the tests pass. That is because it is running the CoreFX tests that do not have your change (and it appears there is a test for it)

Assert.Throws() Failure\r\nExpected: typeof(System.ArgumentException)\r\nActual: typeof(System.ArgumentNullException): Value cannot be null. (Parameter 'culture')\r\n---- System.ArgumentNullException : Value cannot be null. (Parameter 'culture')

Stack trace
   at System.StringComparer.Create(CultureInfo culture, CompareOptions options) in /_/src/System.Private.CoreLib/shared/System/StringComparer.cs:line 64
   at System.Tests.StringComparerTests.<>c.<CreateCultureOptions_InvalidArguments_Throws>b__7_0() in /_/src/System.Runtime/tests/System/StringComparerTests.netcoreapp.cs:line 15
----- Inner Stack Trace -----
   at System.StringComparer.Create(CultureInfo culture, CompareOptions options) in /_/src/System.Private.CoreLib/shared/System/StringComparer.cs:line 64
   at System.Tests.StringComparerTests.<>c.<CreateCultureOptions_InvalidArguments_Throws>b__7_0() in /_/src/System.Runtime/tests/System/StringComparerTests.netcoreapp.cs:line 15

[danmoseley]

We're planning to merge the corefx/coreclr repos so this coordination problem will go away at that point.