public static IEnumerable <IPropertySymbol> GetIndexers(this INamespaceOrTypeSymbol symbol)
 {
     return(symbol == null
         ? SpecializedCollections.EmptyEnumerable <IPropertySymbol>()
             : symbol.GetMembers(WellKnownMemberNames.Indexer).OfType <IPropertySymbol>().Where(p => p.IsIndexer));
 }