@Nonnull
    public static <T extends Cancellable> Predicate<T> ignoreNotCancelled() {
        return (Predicate<T>) IGNORE_UNCANCELLED;
    }
Returns a predicate which only returns true if the event is cancelled

@param <T> the event type
@return a predicate which only returns true if the event is cancelled
helper/src/main/java/me/lucko/helper/event/filter/EventFilters.java