Mongoose, populate where an ID is specific to a project reference

I m trying to populate a mongoose model where I only want the returned items to be the ones that are matched with an ID.

//Partial Schema

task: [{
    projectID: {
      type: String
    },
    theTask: {
      type: Schema.Types.ObjectId,
      ref: "Task" 
    }
  }]

How can I only get the task populated where the projectID is equal to a specific ID. I tried

User.findById({ "_id": req.params.id }).populate({ path: 'task', match: {projectID: req.params.pID}, select: 'theTask' })
  .exec(function(err, docs){
    console.log("POPULATE TASKS DOCS", docs)

But this is showing that the docs is empty.

via henhen