code: @Nullable
      @SuppressWarnings("unchecked")
      public static <T extends Executor> T unwrap(@Nullable T executor) {
          if (!isTtlWrapper(executor)) return executor;
  
          return (T) ((ExecutorTtlWrapper) executor).unwrap();
      }
docs: Unwrap TTL wrapper executor to the original/underneath one.
  <p>
  if the parameter executor is TTL wrapper, return the original/underneath executor;
  otherwise, just return the input parameter executor.
  <p>
  NOTE: if input executor is {@code null}, return {@code null}.
  
  @param executor input executor
  @param <T>      Executor type
  @see #getTtlExecutor(Executor)
  @see #getTtlExecutorService(ExecutorService)
  @see #getTtlScheduledExecutorService(ScheduledExecutorService)
  @see #isTtlWrapper(Executor)
  @since 2.8.0