/**
  * Compares to work packages after the successors.
  *
  * @param ap1 The first work package.
  * @param ap2 The second work package which has to compare with the first one.
  * @return a negative integer, zero, or a positive integer as the first argument is less than,
  *     equal to, or greater than the second.
  */
 @Override
 public final int compare(final Workpackage ap1, final Workpackage ap2) {
   if (WpManager.getFollowers(ap1) != null && WpManager.getFollowers(ap2) != null) {
     return WpManager.getFollowers(ap1).size() - WpManager.getFollowers(ap2).size();
   } else if (WpManager.getFollowers(ap1) == null && WpManager.getFollowers(ap2) == null) {
     return 0;
   } else if (WpManager.getFollowers(ap1) == null) {
     return 1;
   } else {
     return -1;
   }
 }