Bull passing error.cause to failed handlers

Created by: gabegorelick

Description

When failing a job with an Error, Bull attempts to grab the error's cause:

https://github.com/OptimalBits/bull/blob/cf2c6883fc2d861397bd59df7186b730800655e0/lib/queue.js#L1026-L1027

However, there's no guarantee cause will be an instance of Error. In fact, if you pass a VError, cause will be a function that returns the cause. This causes (no pun intended) Bull to pass incorrect values to any failed handler.

I'm also not sure why Bull would want to return the cause and obscure the higher level error in the first place. If I'm passing a wrapped Error as the failure, surely that means I want that error to be returned, and not the lower level error. EDIT: there's a handy test case that explains the rationale: https://github.com/OptimalBits/bull/blob/cf2c6883fc2d861397bd59df7186b730800655e0/test/test_queue.js#L1213

Minimal, Working Test code to reproduce the issue.

const Queue = require('bull');
const VError = require('verror');

const queue = new Queue('foo');
queue.process('job', (job, callback) => {
    callback(new VError(new Error('root cause'), 'wrapper message'));
});
queue.on('failed', (job, err) => {
    console.log(err.stack); // prints `undefined`
    process.exit();
});

queue.add('job', {});

Bull version

3.4.8