public static boolean equalSets(Collection<?> c1, Collection<?> c2) {
    if (c1 == null) {
      return c2 == null;
    }
    else if (c2 == null) {
      return false;
    }

    if (c1.size() != c2.size()) {
      return false;
    }

    HashSet<Object> set = new HashSet<>(c1);
    set.removeAll(c2);
    return (set.size() == 0);
  }
public static boolean equalSets(Collection<?> c1, Collection<?> c2)