Fragment Lollipop Transitions

Question

I have set up fragment transitions on entering and exiting the fragment. And when ever I press back android throws this error:

NullPointerException: Attempt to invoke virtual method getAllowReturnTransitionOverlap() on a null object reference.

This is my code to add slide transitions to fragments. Anyone know why I'm getting this error? I have an activity that holds a fragment. I replace fragments and add them to the backstack. I have a few activities which hold all the fragments in the application.

if ( AndroidUtils.isMinimumSdkLevel( android.os.Build.VERSION_CODES.LOLLIPOP ) )
    {
      if ( enter == null )
      {
        enter = new Slide();
        enter.setDuration( 400 );
        enter.setInterpolator( new DecelerateInterpolator() );
      }

      if ( exit == null )
      {
        exit = new Slide();
        exit.setDuration( 400 );
        exit.setInterpolator( new DecelerateInterpolator() );
      }

      fragment.setEnterTransition( enter );
      fragment.setReturnTransition( exit );
    }