Firebase collection not updating

I have a firebase collection that is not updating on my post call when calling in postman. screamData.comments is not getting populated, and therefore the collection is not updating. Expected result is that the comments collection in firebase gets updated with the comments linked to the screamId.

    exports.getScream = (req, res) => {
    let screamData = {};
    db.doc(`/screams/${req.params.screamId}`)
      .get()
      .then((doc) => {
        if (!doc.exists) {
          return res.status(404).json({ error: 'Scream not found' });
        }
        screamData = doc.data();
        screamData.screamId = doc.id;
        return db
          .collection('comments')
          //.orderBy('createdAt', 'desc')
          .where('screamId', '==', req.params.screamId)
          .get()
          console.log(db.collection('comments'))
      })  
      .then((data) => {
        screamData.comments = [];
        data.forEach((doc) => { 
          screamData.comments.push(doc.data());
        });
        //console.log(screamData)
        return res.json(screamData);
      })

      .catch((err) => {
        console.error(err);
        res.status(500).json({ error: err.code });
      });
}

postman response:

 {
    "createdAt": "2019-07-08T17:25:50.213Z",
    "userHandle": "bobby boi",
    "body": "taha body ",
    "screamId": "BBI6Kqrno3RPURUASwL9",
    "comments": [] //this is what needs to be udpated
}