Android Kotlin How to Get Records from Firebase

Question

I am a beginner in android programming with Kotlin. I'm close on this, but missing something. Google is not showing me just what I need. Hoping someone here can.

I'm using android studio 4.1.1, kotlin and Firebase

I have several records in my test Firebase database.

each of these records has data, but when I use println in my code one part is showing null and it is not hitting another println at all.

my code - in part

WeightExercise.kt:

...
// i write records to the db like this:

val ref = FirebaseDatabase.getInstance().getReference("weights")
        val recordID = ref.push().key
        val userId = Global.userID

       if (recordID != null){
            ref.child(userId).child(recordID).setValue(weight).addOnCompleteListener{
                Toast.makeText(applicationContext,"Weight Record rated successfully",Toast.LENGTH_LONG).show()
            }
        }
...

DisplayWeightsActivity.kt:

val uid = FirebaseAuth.getInstance().currentUser!!.uid
val ref = FirebaseDatabase.getInstance().getReference("weights")
val uidRef = ref.child("weights").child(uid)
val valueEventListener = object : ValueEventListener {
    override fun onDataChange(dataSnapshot: DataSnapshot) {
       println("$$$$$$ dataSnapshot: ${dataSnapshot.toString()}")
       for (ds in dataSnapshot.children) {
           println("#$#$#$#$#$  in override dataSnapshot.children")
           val muscle = ds.child("muscleGroup").getValue(String::class.java)
           val exercise = ds.child("exerciseText").getValue(String::class.java)
           val date = ds.child("date").getValue(String::class.java)
           Log.d("TAG", date + " " + muscle + " " + exercise)
       }
    }

    override fun onCancelled(databaseError: DatabaseError) {
       Log.d("DB ERROR", databaseError.message) //Don't ignore errors!
    }
    uidRef.addListenerForSingleValueEvent(valueEventListener)
}

In my Logcat window I see this:

$$$$$$ dataSnapshot: DataSnapshot { key = oB3pzvhAr6foyhGZUuvFl4CECOw2, value = null }

But the println("#$#$#$#$#$ in override dataSnapshot.children") does not print.

The key above oB3pzv... matches my userid, so it sees that. I'm not sure what value = null means. Is it not seeing the children records? How do I get the children records under weights >> userId ?