get(e) {
    var t;
    return (t = this.map.get(e)) !== null && t !== void 0 ? t : [];
  }
Returns an array of all values associated with the given key. If no value exists,
an empty array is returned.

_Note:_ The returned array is assumed not to be modified. Use the `set` method to add a
value and `delete` to remove a value from the multimap.