code: @NonNull
      public Set<Job> getAllJobsForTag(@NonNull String tag) {
          return mJobExecutor.getAllJobsForTag(tag);
      }
docs: Jobs are cached in memory even if they already have finished. But finished jobs are never
  restored after the app has relaunched. Since finished jobs could cause memory leaks, they wrapped
  inside of a {@link WeakReference} and can be removed from memory. If you need to know the results
  of finished jobs or whether a job has been run, you can call {@link #getAllJobResults()}.
  
  @param tag The tag of the running or finished jobs.
  @return A duplicate {@link Set} containing all running and cached finished jobs associated with
  this tag or an empty set. Never returns {@code null}. The set may be modified without direct
  effects to the actual backing store.