docs: public boolean containsKey(Object key) {
      FastHashtableEntry tab[] = table;
      int hash = key.hashCode();
      int index = (hash & 0x7FFFFFFF) % tab.length;
      for (FastHashtableEntry e = tab[index] ; e != null ; e = e.next) {
        if ((e.hash == hash) && e.key.equals(key)) {
          return true;
        }
      }
      return false;
    }