docs: public static <K,E> Map<K, Integer> countBy(Iterator<E> self, @ClosureParams(FirstParam.FirstGenericType.class) Closure<K> closure) {
          Map<K, Integer> answer = new LinkedHashMap<K, Integer>();
          while (self.hasNext()) {
              K value = closure.call(self.next());
              countAnswer(answer, value);
          }
          return answer;
      }