code: public T match(I item)
      {
          Set<T> set = mapSet.get(item);
          if (set.size() == 1)
          {
              T match = set.iterator().next();
              unmap(match);
              return match;
          }
          return null;
      }
docs: Returns target if item match. Otherwise returns null.
  Matched targets mappings are removed.
  @param item
  @return