code: @Override
    public int onStartCommand(final Intent intent, int flags, final int startId) {
      Timber.v("onStartCommand called.");
      if (intent != null) {
        final OfflineDownloadOptions offlineDownload = intent.getParcelableExtra(KEY_BUNDLE);
        if (offlineDownload != null) {
          onResolveCommand(intent.getAction(), offlineDownload);
        } else {
          stopSelf(startId);
          throw new NullPointerException("A DownloadOptions instance must be passed into the service to"
              + " begin downloading.");
        }
      }
      return START_STICKY;
    }
docs: Called each time a new download is initiated. First it acquires the
  {@link OfflineDownloadOptions} from the intent and if found, the process of downloading the
  offline region carries on to the {@link #onResolveCommand(String, OfflineDownloadOptions)}.
  If the {@link OfflineDownloadOptions} fails to be found inside the intent, the service is
  stopped (only if no other downloads are currently running) and throws a
  {@link NullPointerException}.
  <p>
  {@inheritDoc}
  
  @since 0.1.0