@NonNull
    public static List<TtlRunnable> gets(@Nullable Collection<? extends Runnable> tasks) {
        return gets(tasks, false, false);
    }
wrap input {@link Runnable} Collection to {@link TtlRunnable} Collection.

@param tasks task to be wrapped. if input is {@code null}, return {@code null}.
@return wrapped tasks
@throws IllegalStateException when input is {@link TtlRunnable} already.
ttl2-compatible/src/main/java/com/alibaba/ttl/TtlRunnable.java