ES 6.x: Content-Type header is missing

[sagimann]

Hi, I can't seem to use the module (v6.8.8), steps to reproduce below:

// env on Elastic Beanstalk EC2 machine:
npm i @elastic/elasticsearch@6
export AWS_REGION='xx-xxxx-1'
export ES_ENDPOINT='https://.../'

// code:
const ES = require('@elastic/elasticsearch');
const { createConnector } = require('aws-elasticsearch-js');
_es = new ES.Client({
    node: process.env.ES_ENDPOINT,
    Connection: createConnector()
});
const q = {
    "index": "lyrics_catalog",
    "type": "_doc",
    "size":1,
    "body": {
        "query": {
            "match_all":{}
       }
    }
}
_es.search(q).then(console.log, console.error)

// output:
Promise {
  <pending>,
  [Symbol(async_id_symbol)]: 3468,
  [Symbol(trigger_async_id_symbol)]: 3465,
  [Symbol(destroyed)]: { destroyed: false }
}
> ResponseError: Response Error
    at IncomingMessage.<anonymous> (/xxx/node_modules/@elastic/elasticsearch/lib/Transport.js:310:25)
    at IncomingMessage.emit (node:events:532:35)
    at IncomingMessage.emit (node:domain:537:15)
    at endReadableNT (node:internal/streams/readable:1346:12)
    at processTicksAndRejections (node:internal/process/task_queues:83:21) {
  meta: {
    body: { error: 'Content-Type header is missing', status: 406 },
    statusCode: 406,
    headers: {
      date: 'Sun, 27 Feb 2022 16:06:53 GMT',
      'content-type': 'application/json; charset=UTF-8',
      'content-length': '55',
      connection: 'keep-alive',
      'access-control-allow-origin': '*'
    },
    warnings: null,
    meta: {
      context: null,
      request: [Object],
      name: 'elasticsearch-js',
      connection: [Object],
      attempts: 0,
      aborted: false
    }
  }
}

Note that adding headers option to the ES client (as described here) breaks the initialization with another error:

Uncaught TypeError: Cannot read properties of undefined (reading 'username')
    at getAuth (/xxx/node_modules/@elastic/elasticsearch/index.js:231:16)
    at new Client (/xxx/node_modules/@elastic/elasticsearch/index.js:70:23)