@Override
 public int compare(WordSimilarity o1, WordSimilarity o2) {
   if (Double.isNaN(o1.getSimilarity()) && Double.isNaN(o2.getSimilarity())) {
     return 0;
   } else if (Double.isNaN(o1.getSimilarity()) && !Double.isNaN(o2.getSimilarity())) {
     return -1;
   } else if (!Double.isNaN(o1.getSimilarity()) && Double.isNaN(o2.getSimilarity())) {
     return 1;
   }
   return Double.compare(o2.getSimilarity(), o1.getSimilarity());
 }