public CSharpSymbolMap(NonMissingModuleSymbol module)
 {
     if (module == null)
     {
         throw new ArgumentNullException(nameof(module));
     }
     _module = module;
 }
 internal CSharpNamedTypeSymbol(NonMissingModuleSymbol module, CSharpSymbols.NamedTypeSymbol csharpSymbol)
 {
     _module       = module;
     _csharpSymbol = csharpSymbol;
 }