code: @CheckForNull
      public WorkUnit getCurrentWorkUnit() {
          lock.readLock().lock();
          try {
              return workUnit;
          } finally {
              lock.readLock().unlock();
          }
      }
docs: Returns the current {@link WorkUnit} (of {@link #getCurrentExecutable() the current executable})
  that this executor is running.
  
  @return
  null if the executor is idle.