docs: @Nullable
      public static TtlTimerTask get(@Nullable TimerTask timerTask, boolean releaseTtlValueReferenceAfterRun, boolean idempotent) {
          if (null == timerTask) return null;
  
          if (timerTask instanceof TtlEnhanced) {
              // avoid redundant decoration, and ensure idempotency
              if (idempotent) return (TtlTimerTask) timerTask;
              else throw new IllegalStateException("Already TtlTimerTask!");
          }
          return new TtlTimerTask(timerTask, releaseTtlValueReferenceAfterRun);
      }