ログイン後に Firebase データが Android ListView に表示されないのはなぜですか?

public void makeItem ()
{
    lv = findViewById(R.id.listView);
    db = FirebaseDatabase.getInstance().getReference();
    helper = new FirebaseHelper(db);
    adapter= new AdapterItem(this,helper.retrive());
    lv.setAdapter(adapter);
}

public AdapterItem(Context c, ArrayList<CustomListAdapter> customListAdapters) {
    this.c = c;
    this.customListAdapters = customListAdapters;
}

private String ItemName; // Field in CustomListAdapter class

ItemName.setText(CLA.getItemName()); // Getter in AdapterItem class

public class CustomListAdapter {
    private String itemName, quantity, serialNo, supplierName, supplierEmail, supplierPhone;
}

@PropertyName("ItemName")
public String getItemName() { return ItemName; }