docs: public ClassicCounter<K2> setCounter(K1 o, Counter<K2> c) {
      ClassicCounter<K2> old = getCounter(o);
      total -= old.totalCount();
      if (c instanceof ClassicCounter) {
        map.put(o, (ClassicCounter<K2>) c);
      } else {
        map.put(o, new ClassicCounter<K2>(c));
      }
      total += c.totalCount();
      return old;
    }