pouchdb-find error with elemMatch and array of objects

testfind.js

#!/usr/bin/env node

var async = require('async')
var PouchDB = require('pouchdb')
PouchDB.plugin(require('pouchdb-find'))

var db = PouchDB('foobar')

async.series([
  // drop database and re-create (always start with new database)
  function (callback) {
    db.destroy(function (err) {
      if (err) {
        throw(err)
      }

      db = PouchDB('foobar')
      
      callback()
    })
  },

  // fill database
  function (callback) {
    async.parallel([
      function (callback) {
        db.put({ _id: "1", comments: [ { user: 'alice', date: '2017-01-01' }, { user: 'bob', date: '2017-01-02' } ] }, function (err) {
          if (err) { throw(err) }
          callback()
        })
      },
      function () {
        db.put({ _id: "2", comments: [ { user: 'alice', date: '2017-01-01' }, { user: 'charly', date: '2017-01-03' } ] }, function (err) {
          if (err) { throw(err) }
          callback()
        })
      }
    ],
    function () {
      callback()
    })
  },

  // now query
  function (callback) {
    db.find({ selector: { 'comments': { '$elemMatch': { 'user': 'charly' }}}}, function (err, result) {
      if (err) { throw(err) }
      callback()
    })
  }
])