code: public void setAdPresets(Collection<BannerAdPreset> adPresets) {
          Collection<BannerAdPreset> mAdPresets = adPresets==null||adPresets.size() == 0
                  ? Collections.singletonList(BannerAdPreset.DEFAULT)
                  :adPresets;
          mAdPresetCyclingList.clear();
          mAdPresetCyclingList.addAll(mAdPresets);
      }
docs: Sets an unit IDs for admob banners.
  It works like cycling FIFO (first in = first out, cycling from end to start).
  Each ad block will get one from the queue.
  If the desired count of ad blocks is greater than this collection size
  then it will go again to the first item and iterate as much as it required.
  ID should be active, please check it in your Admob's account.