code: public static <T extends Elements> Predicate<T> forExistence() {
          return Predicates.not(WaitPredicates.<T>forUnexistence());
      }
docs: Predicate to use with {@link WaitWebElements#wait(Predicate)} methods which ensures that
  evaluation will only be successful when this instance is empty (that is, evaluates
  to zero {@link org.openqa.selenium.WebElement} instances).
  
  @param <T> the generic type
  @return predicate that returns true if it is empty