ObjectId and aggregation returns nothing

This is my aggregation pipelines:

db.articles.aggregate([ { '$match': { _id: ObjectId('5422d579466673f01a84c82f') } },
  { '$unwind': '$comments' },
  { '$project':
     { content: '$comments.content',
       author: '$comments.author',
       created_at: '$comments.created_at',
       _id: '$comments._id',
       article: '$_id' } },
  { '$skip': 0 },
  { '$limit': 15 },
  { '$match': {} } ])

This returns:

/* 0 */
{
    "result" : [ 
        {
            "_id" : ObjectId("5422d5a9466673f01a84c830"),
            "created_at" : ISODate("2014-09-24T14:31:05.644Z"),
            "article" : ObjectId("5422d579466673f01a84c82f")
        }, 
        {
            "_id" : ObjectId("5422d5b4466673f01a84c831"),
            "content" : "foo",
            "created_at" : ISODate("2014-09-24T14:31:16.606Z"),
            "article" : ObjectId("5422d579466673f01a84c82f")
        }
    ],
    "ok" : 1
}

This works well using Robomongo. My nodejs code:

 pipelines = [ 
  {
    $match: {_id: id}
  },
  {
    $unwind: "$#{@location}"
  },
  {
    $project: project
  },
  {
    $skip: query.skip or query.offset or 0
  },
  {
    $limit: query.limit or 15
  },
  if query.sort then {
    $sort: if query.sort and query.sort[0] is '-'
      obj = {}
      obj[query.sort.substring(1)] = -1
      obj
    else if query.sort
      obj = {}
      obj[query.sort] = 1
      obj
  },
  {
    $match: match
  }
]

@model.aggregate _.compact(pipelines), (err, result) ->
  if err then return deferred.reject err
  deferred.resolve result

The id is like this (model.schema.paths._id.options.type)(query.article) (because I don't have access to mongoose, only the model.

The pipelines sent are like this:

[ { '$match':
     { _id:
        { path: '5422d579466673f01a84c82f',
          instance: 'ObjectID',
          validators: [],
          setters: [],
          getters: [],
          options: undefined,
          _index: null } } },
  { '$unwind': '$comments' },
  { '$project':
     { content: '$comments.content',
       author: '$comments.author',
       created_at: '$comments.created_at',
       _id: '$comments._id',
       article: '$_id' } },
  { '$skip': 0 },
  { '$limit': 15 },
  { '$match': {} } ]

And if I just set the id as a string (without ObjectId constructor), it doesn't works either. If I remove the first pipeline ($match) it works (but I want it with this pipeline). Hope I'm clear.