Retrieving subscriptions fails with message: Error fetching subscriptions: TypeError: e.json is not a function

[andreban]

This seems to happen when a user hasn't authorised notifications and doesn't have a token yet. The promise chain seems to be broken. Something like the below will fix it.

getSubscriptions() {
    const messaging = firebase.messaging();
    return messaging.getToken()
      .then(token => {
        if (!token) {
          return Promise.resolve([]);
        }
        const url = TOPICS_ENDPOINT + '?token=' + token;
        return fetch(url, { headers: { Accept: 'application/json' }})
          .then(response => {
            return response.json();
          })
          .then(json => {
            return json.subscriptions;
          })
          .catch(err => {
            console.error('Error fetching subscriptions: ', err);
            return Promise.resolve([]);
          });;
      });
  }