Resolving wrong overloaded method when having variable arguments

import java.util.Comparator;

class Foo<T> {}

class Bar<T> {
  static <T> Bar<T> concat(Bar<? extends T>... x)  { return null; }
  static <T> Bar<T> concat(Bar<? extends Bar<? extends T>> x)  { return null; }
  void toSortedSet(Comparator<? super T> x) {}
}

class Main {
  static final void test() {
    Bar<Foo<Number>> x = null;
    Comparator<Foo<Number>> y = null;
    Bar.concat(x).toSortedSet(y);
  }
}

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
groovy35.groovy: 15: [Static type checking] - Cannot call <T> Bar#concat(Bar<? extends Bar<? extends T>>) with arguments [Bar<Foo<java.lang.Number>>]
 @ line 15, column 15.
       Bar.concat(x).toSortedSet(y);
                 ^

groovy35.groovy: 15: [Static type checking] - Cannot find matching method java.lang.Object#toSortedSet(java.util.Comparator<Foo<java.lang.Number>>). Please check if the declared type is correct and if the method exists.
 @ line 15, column 5.
       Bar.concat(x).toSortedSet(y);
       ^

2 errors

import com.google.common.collect.*;
import java.util.Comparator;

class Foo<K> {}

class Main {
  static final void test() {
    Iterable<? extends Foo<Number>> x = null;
    Comparator<? super Foo<Number>> y = null;
    FluentIterable.concat(x).toSortedSet(y);

  }
}