has(e, t) {
    if (t === void 0)
      return this.map.has(e);
    {
      const r = this.map.get(e);
      return r ? r.indexOf(t) >= 0 : !1;
    }
  }
Operates differently depending on whether a `value` is given:
 * With a value, this method returns `true` if the specific key / value pair is present in the multimap.
 * Without a value, this method returns `true` if the given key is present in the multimap.