UnhandledPromiseRejectionWarning when using with bulk helper

[zoellner]

The warning below is logged when using this lib with the es.helpers.bulk function

Sample code:

  const syncedAt = new Date().toISOString();
  const bulkResult = await es.helpers.bulk({
    datasource: [{syncedAt, id: '1'}],
    onDocument(doc) {
      return {index: {_index: 'test-index', _id: doc.id}};
    }
  });
  console.log(bulkResult);

Note that it works fine for other es requests, e.g. const searchResult = await es.search({index: 'test-index', body: {query: {match_all: {}}}});

I've debugged this a bit and it seems that even the most simple custom transport class using a promise will lead to this error which makes me think that the current approach with a promise inside the Transport.request function doesn't work

class CustomTransport extends Transport {
  request (params, options, callback) {
    new Promise((resolve) => {
      resolve();
    })
    .then(() => super.request(params, options, callback));
  }
}

The logged warning:

    at Object.then (/Users/zoellner/bc-books/bcb-server-api/node_modules/@elastic/elasticsearch/lib/Transport.js:337:18)
(node:36053) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:36053) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

[lobeck]

Is there any workaround available for this?