Case constant causing Crash?

[DavePearce]

Dafny version

4.1.0

Code to produce this issue

module Gas {
    type State = ()
    const STATICCALL : nat := 0xfa

    function f(op: nat, s: State): State
    {
        match op
            case STATICCALL => s
            case _ => s
    }
}

Command to run and resulting output

dafny-4.1/dafny BugTest.dfy

What happened?

Unhandled exception. System.AggregateException: One or more errors occurred. (Value cannot be null. (Parameter 'source'))
 ---> System.ArgumentNullException: Value cannot be null. (Parameter 'source')
   at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Linq.Enumerable.Select[TSource,TResult](IEnumerable`1 source, Func`2 selector)
   at Microsoft.Dafny.Substituter.<>c__DisplayClass7_1.<Substitute>g__SubstituteForPattern|0(ExtendedPattern pattern)
   at Microsoft.Dafny.Substituter.Substitute(Expression expr)
   at Microsoft.Dafny.Translator.GetFunctionAxiom(Function f, Expression body, List`1 lits)
   at Microsoft.Dafny.Translator.AddFunctionAxiom(Function boogieFunction, Function f, Expression body)
   at Microsoft.Dafny.Translator.AddClassMember_Function(Function f)
   at Microsoft.Dafny.Translator.AddFunction_Top(Function f, Boolean includeAllMethods)
   at Microsoft.Dafny.Translator.AddClassMembers(TopLevelDeclWithMembers c, Boolean includeAllMethods, Boolean includeInformationAboutType)
   at Microsoft.Dafny.Translator.AddTypeDecl(RevealableTypeDecl d)
   at Microsoft.Dafny.Translator.DoTranslation(Program p, ModuleDefinition forModule)
   at Microsoft.Dafny.Translator.Translate(Program p, ErrorReporter reporter, TranslatorFlags flags)+MoveNext()
   at Microsoft.Dafny.DafnyDriver.Translate(ExecutionEngineOptions options, Program dafnyProgram)+MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Microsoft.Dafny.DafnyDriver.ProcessFilesAsync(IList`1 dafnyFiles, ReadOnlyCollection`1 otherFileNames, ErrorReporter reporter, Boolean lookForSnapshots, String programId)
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at Microsoft.Dafny.DafnyDriver.ThreadMain(String[] args)
   at Microsoft.Dafny.DafnyDriver.<>c__DisplayClass10_0.<Main>b__0()
   at System.Threading.Thread.StartCallback()
Aborted (core dumped)

I should add this this code compiled without problem on Dafny 4.0.

What type of operating system are you experiencing the problem on?

Linux