parse-server aggregate function returns empty object

[shash7976]

New Issue Checklist

• [X] I am not disclosing a vulnerability.
• [X] I am not just asking a question.
• [X] I have searched through existing issues.
• [X] I can reproduce the issue with the latest version of Parse Server.

Issue Description

$lookup is unable to grab the order object in spite of having an order that particular _id.

If I remove the $group and try $lookup directly I'm able to get the orderObject. (objectId: '$_p_order', and objectId:'$order' produces the same result)

EventTracking consists of order(pointer object), action(string)

Steps to reproduce

 const startingFrom = new Date(new Date() - 7 * 60 * 60 * 24 * 1000)
    const pipeline = [{
        match: {
            action: {
                $in: [
                    'Status updated from: Paid to Approved',
                    'Status updated from: Approved to Ready'
                ]
            },
            createdAt: { $gte: startingFrom }
        }
    },
    {
        group: {
            objectId: '$_p_order',
            date: {
                $addToSet: '$createdAt'
            },
        }
    },
    {
        addFields: {
            size: {
                $size: '$date'
            },
        }
    },
    {
        match: {
            size: {
                $eq: 2
            }
        }
    },
    {
        lookup: {
            'from': 'Order',
            'localField': 'objectId',
            'foreignField': '_id',
            'as': 'OrderObject'
        }
    }]
try {
        const query = new Parse.Query('EventTracking');
        const result = await query.aggregate(pipeline, master);
        console.log(result);
  } catch (error) {
      console.log(error);
}

Actual Outcome

  {
    date: [ [Object], [Object] ],
    size: 2,
    OrderObject: [],
    objectId: '9UpnIHbG8n'
  },

Expected Outcome

  {
    date: [ [Object], [Object] ],
    size: 2,
    OrderObject: [Object],
    objectId: '9UpnIHbG8n'
  },

Environment

Server

• Parse Server version: 4.10.3
• Operating system: Ubuntu 18.04
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): AWS

Database

• System (MongoDB or Postgres): MongoDB
• Database version: 4.4
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): MongoDB Atlas

Client

• SDK (iOS, Android, JavaScript, PHP, Unity, etc): JavaScript
• SDK version: FILL_THIS_OUT

Logs

[parse-github-assistant[bot]]

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[mtrezza]

Can you please complete the template and reduce the example to a minimum to reproduce the issue. It would also be helpful if you could open a PR with a failing test to demo the issue.