The method map(Function<? super List<? extends SchemaComponent>,? extends R>) in the type 
Stream<List<? extends SchemaComponent>> is not applicable for the arguments (((fun2 == null) ? 
SchemaTypeSystemImpl::buildComponentRefMap : fun2))
The type of buildComponentRefMap(List<? extends SchemaComponent>) from the type 
SchemaTypeSystemImpl is Map<QName,SchemaComponent.Ref>, this is incompatible with the 
descriptor's return type: R