Alexa Audio Player problem with Promise

audioHandler.js

let handlers = {
  'PlayAudio_NG': function() {
    let get_url = () => {
      return new Promise((resolve) => {
        ...
        resolve(url);  // S3のObjectのURLを返す
      });
    }

    let self = this;
    get_url().then((url) => {
      self.response.speak('再生します').audioPlayerPlay('REPLACE_ALL', url, url, null, 0);
      self.emit(':responseReady');
    });
  },
  'PlayAudio_OK': function() {
    let url = 'https://s3-ap-northeast-1.amazonaws.com/hoge/sample.mp4';
    this.response.speak('再生します').audioPlayerPlay('REPLACE_ALL', url, url, null, 0);
    this.emit(':responseReady');
  }
}