Resolve ambiguous method reference

[pkeller]

When importing the XMLBeans code into Eclipse, I get the following compile-time errors at this line:

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

This may well be a quirk of the Eclipse compiler, that it can't resolve ambiguous method references except as a simple argument to the map function, but switching to a lambda seems harmless to me and will help people who use Eclipse to examine the XMLBeans code.