You could extend `SimpleTypeVisitor6` instead of `AbstractTypeVisitor6`, so you'd only have to implement the "interesting" methods.

I'm also wondering whether we should return `Boolean` from the methods instead of using the shared variable in the outer class? If sticking to the current approach, we could parameterize the visitor type with `Void` for `R` instead of `TypeMirror` in order to make apparent that the return value is never used.