VarInfoName.java

public abstract class VarInfoName {

    public abstract <T extends Object> T accept(Visitor<T> v);

    public abstract static class Visitor<T extends Object> {}

    public abstract static class BooleanAndVisitor extends Visitor<Boolean> {
        private boolean result;

        public BooleanAndVisitor(VarInfoName name) {
            //:: error: (argument.type.incompatible) :: warning: (known.nonnull)
            result = (name.accept(this) != null);
        }
    }
}