Firebase Android failed to convert HashMap to String

I am getting an error while retriving data from Firebase in Android app.

Error here.

My code:

DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();
    DatabaseReference ref = databaseReference.child(path);

    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            String value = dataSnapshot.getValue(String.class);

            ClipboardManager clipboard = (ClipboardManager) getApplicationContext().getSystemService(CLIPBOARD_SERVICE);
            clipboard.setText(value);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {


        }

"path" - child's name.

And my Firebase Database