Node.js stream of objects from MongoDB

Question

I have a collection inside MongoDB with thousands of documents. A document should be processing depending on some logic. To make the point simple, I suppose here there is a field requiresProcessing indicating whether or not the document must be processed.

To do the processing I created a stream of objects from MongoDB to stream just the objects that must be processed. The code is as follows:

// MongoDB repository module
var config = require('./configurations.js');
var db = require('monk')(config.mongodb.connectionUrl);
var collection = db.get('collection');

var numForProcessing = 0;

var getNextForProcessing = function() {
    numForProcessing++;
    return collection.find({requiresProcessing: true}, {skip: numForProcessing - 1, limit: 1}).then(function(data) {
        return data[0];
    });
}

module.exports = {
    getNextForProcessing: getNextForProcessing
};

// Stream Definition Module
"use strict";

const Readable = require('stream').Readable;
const repository = require('./repository.js');

class StreamObjectsForProcessing extends Readable {

    constructor(options) {
        if (options === undefined) options = {};

        options.objectMode = true;
        super(options);
    }

    _read() {
        let self = this;

        repository.getNextForProcessing().then(function(data) {
            if (data === undefined) {
                self.push(null);
            } else {
                self.push(data);
            }
        }).catch(function(err) {
            console.log(err);
        });
    }
}

Then to use it, I simply do as usual:

var stream = new StreamObjectsForProcessing();
stream.on('data', function(data) {
    // processing here
});

Although it is working, I want a review for this. Is it a good approach? Or can it be improved?