docs: private void initFragment() {
          FragmentManager fm = getSupportFragmentManager();
          if (fm.findFragmentByTag(FragmentTransitionDefaultFragment.FRAGMENT_TAG) == null) {
              FragmentTransaction ft = fm.beginTransaction();
              ft.add(R.id.fragment, new FragmentTransitionDefaultFragment(), FragmentTransitionDefaultFragment.FRAGMENT_TAG);
              ft.commit();
              fm.executePendingTransactions();
          }
      }