How to get a string in ObjectId in MongoDB v3.6?

Working with Data
1

[ Question ]
I have an aggregation query whose MongoDB repsonse is :

...
_id: ObjectId('5e822d6c87502b3a9b751786')
...

I would like to get the string inside the ObjectId which is 5e822d6c87502b3a9b751786.

[ Problem ]
I have searched this question but so far there are only two operators which are $toString and $toObjectId :

$project: {
      _id: {
        $toString: "$_id"
      }
}

$project: {
      _id: {
        $toObjectId: "$_id"
      }
}

MongoDB v3.6 does not support them if I am not mistaken.
Is there any workaround in MongoDB v3.6 to get a string inside an ObjectId?

Any help is much appreciated :slight_smile: