尝试在空对象引用上调用虚拟方法'int java.lang.Long.intValue（）'-当我尝试在onCreate上调用该方法时

Question

当我将此方法放在onCreate上时，我给了我这个错误 java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'int java.lang.Long.intValue（）'

im试图将当前数据库中的“硬币”总数放入Textview中

public void showtotalcoins(){

    mShowTotalCoins= findViewById(R.id.numerCoinstxt);
    FirebaseFirestore db1= FirebaseFirestore.getInstance();
    DocumentReference showTickets= db1.document("Tickets/TotalTickets");

    showTickets.get().addOnSuccessListener(new 
                    OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {

            coins = documentSnapshot.getLong("Tickets").intValue();
            showTotalCoins= coins*50;
            mShowTotalCoins.setText(""+showTotalCoins);

        }
    });
 }
xml
<TextView
    android:id="@+id/numerCoinstxt"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginTop="8dp"
    android:layout_marginBottom="8dp"
    android:text="-"
    android:textSize="70sp"
    app:layout_constraintBottom_toTopOf="@+id/mticket"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.489"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/TotalCoinx"
    app:layout_constraintVertical_bias="0.496"