@Nullable
    @Contract(value = "null -> null; !null -> !null", pure = true)
    @SuppressWarnings("unchecked")
    public static <T> T unwrap(@Nullable T obj) {
        if (!isWrapper(obj)) return obj;
        else return ((TtlWrapper<T>) obj).unwrap();
    }
Generic unwrap method, unwrap {@link TtlWrapper} to the original/underneath one.
<p>
this method is {@code null}-safe, when input parameter is {@code null}, return {@code null};
if input parameter is not a {@link TtlWrapper} just return input.

@see TtlWrappers#wrapSupplier(Supplier)
@see TtlWrappers#wrapConsumer(Consumer)
@see TtlWrappers#wrapBiConsumer(BiConsumer)
@see TtlWrappers#wrapFunction(Function)
@see TtlWrappers#wrapBiFunction(BiFunction)
@see TtlRunnable#get(Runnable)
@see TtlCallable#get(java.util.concurrent.Callable) TtlCallable.get(Callable)
@see com.alibaba.ttl3.executor.TtlExecutors#getTtlExecutor(java.util.concurrent.Executor) TtlExecutors.getTtlExecutor(Executor)
@see com.alibaba.ttl3.executor.TtlExecutors#getTtlExecutorService(java.util.concurrent.ExecutorService) TtlExecutors.getTtlExecutorService(ExecutorService)
@see com.alibaba.ttl3.executor.TtlExecutors#getDisableInheritableThreadFactory(java.util.concurrent.ThreadFactory) TtlExecutors.getDisableInheritableThreadFactory(ThreadFactory)
@see com.alibaba.ttl3.executor.TtlExecutors#getDisableInheritableForkJoinWorkerThreadFactory(java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory) TtlExecutors.getDisableInheritableForkJoinWorkerThreadFactory(ForkJoinWorkerThreadFactory)
@see TtlRunnable#unwrap(Runnable)
@see TtlCallable#unwrap(java.util.concurrent.Callable) TtlCallable.unwrap(Callable)
@see com.alibaba.ttl3.executor.TtlExecutors#unwrapTtlExecutor(java.util.concurrent.Executor) TtlExecutors.unwrapTtlExecutor(Executor)
@see com.alibaba.ttl3.executor.TtlExecutors#unwrapDisableInheritableThreadFactory(java.util.concurrent.ThreadFactory) TtlExecutors.unwrapDisableInheritableThreadFactory(ThreadFactory)
@see com.alibaba.ttl3.executor.TtlExecutors#unwrapDisableInheritableForkJoinWorkerThreadFactory(java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory) TtlExecutors.unwrapDisableInheritableForkJoinWorkerThreadFactory(ForkJoinWorkerThreadFactory)
@see com.alibaba.ttl3.executor.TtlExecutors#unwrapTtlRunnableUnwrapComparator(java.util.Comparator) TtlExecutors.unwrapTtlRunnableUnwrapComparator(Comparator)
@see #isWrapper(Object)
ttl-core/src/main/java/com/alibaba/ttl3/TtlWrappers.java