docs: @SafeVarargs
  	public static <T> Collection<T> union(Collection<T> coll1, Collection<T> coll2, Collection<T>... otherColls) {
  		Collection<T> union = union(coll1, coll2);
  		for (Collection<T> coll : otherColls) {
  			union = union(union, coll);
  		}
  		return union;
  	}