NullReferenceException crash in ErrorReporter.Error due to Resolver.CheckIsLvalue

[cpitclaudel]

Input:

method M() {
  b1 :| true;
}

Output:

 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Dafny.ErrorReporter.Error(MessageSource source, Expression e, String msg, Object[] args) in C:\build\Source\Dafny\Reporting.cs:line 95
   at Microsoft.Dafny.Resolver.CheckIsLvalue(Expression lhs, ICodeContext codeContext) in C:\build\Source\Dafny\Resolver.cs:line 13582
   at Microsoft.Dafny.Resolver.ResolveAssignSuchThatStmt(AssignSuchThatStmt s, ICodeContext codeContext) in C:\build\Source\Dafny\Resolver.cs:line 13092
   at Microsoft.Dafny.Resolver.ResolveConcreteUpdateStmt(ConcreteUpdateStatement s, ICodeContext codeContext) in C:\build\Source\Dafny\Resolver.cs:line 12973
   at Microsoft.Dafny.Resolver.ResolveStatement(Statement stmt, ICodeContext codeContext) in C:\build\Source\Dafny\Resolver.cs:line 11174
   at Microsoft.Dafny.Resolver.ResolveStatementWithLabels(Statement stmt, ICodeContext codeContext) in C:\build\Source\Dafny\Resolver.cs:line 13635
   at Microsoft.Dafny.Resolver.ResolveBlockStatement(BlockStmt blockStmt, ICodeContext codeContext) in C:\build\Source\Dafny\Resolver.cs:line 13605
   at Microsoft.Dafny.Resolver.ResolveMethod(Method m) in C:\build\Source\Dafny\Resolver.cs:line 10400
   at Microsoft.Dafny.Resolver.ResolveClassMemberBodies(TopLevelDeclWithMembers cl) in C:\build\Source\Dafny\Resolver.cs:line 9613
   at Microsoft.Dafny.Resolver.ResolveTopLevelDecls_Core(List`1 declarations, Graph`1 datatypeDependencies, Graph`1 codatatypeDependencies, Boolean isAnExport) in C:\build\Source\Dafny\Resolver.cs:line 2821
   at Microsoft.Dafny.Resolver.ResolveModuleDefinition(ModuleDefinition m, ModuleSignature sig, Boolean isAnExport) in C:\build\Source\Dafny\Resolver.cs:line 1035
   at Microsoft.Dafny.Resolver.ResolveProgram(Program prog) in C:\build\Source\Dafny\Resolver.cs:line 507
   at Microsoft.Dafny.Main.Resolve(Program program, ErrorReporter reporter) in C:\build\Source\Dafny\DafnyMain.cs:line 163
   at Microsoft.Dafny.Main.ParseCheck(IList`1 files, String programName, ErrorReporter reporter, Program& program) in C:\build\Source\Dafny\DafnyMain.cs:line 114
   at Microsoft.Dafny.DafnyDriver.ProcessFiles(IList`1 dafnyFiles, ReadOnlyCollection`1 otherFileNames, ErrorReporter reporter, Boolean lookForSnapshots, String programId) in C:\build\Source\DafnyDriver\DafnyDriver.cs:line 301
   --- 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) in C:\build\Source\DafnyDriver\DafnyDriver.cs:line 116
   at Microsoft.Dafny.DafnyDriver.<>c__DisplayClass9_0.<Main>b__0() in C:\build\Source\DafnyDriver\DafnyDriver.cs:line 92
   at System.Threading.Thread.StartCallback()