var flag= admin.firestore().collection('video').doc(thumbnailName);
    var getDoc = flag.get()
        .then(doc => {
          if (doc.exists) {
          console.log('exit process');// data found in firestore exit frm here
      process.exit();
return null;// doesnt work here
          }
          else {
            console.log('create data in firestore');// do some work here
          }
        })
        .catch(err => {
          console.log('Error getting document', err);
        });