При добавление кнопки назад вылетает ошибка

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"

    android:id="@+id/HonorsActivity"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".HonorsActivity">


<androidx.appcompat.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="413dp"
    android:layout_height="58dp"
    android:layout_marginBottom="675dp"
    android:background="@color/colorPrimary"
    android:minHeight="?attr/actionBarSize"
    android:theme="?attr/actionBarTheme"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="1.0" />

<ImageView
    android:id="@+id/imageMenu1"
    android:layout_width="30dp"
    android:layout_height="30dp"

    android:layout_marginStart="16dp"

    android:contentDescription="@string/app_name"
    android:src="@drawable/ic_menu_book"
    app:layout_constraintBottom_toBottomOf="@+id/toolbar"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="@+id/toolbar"
    app:tint="@color/white" />


</androidx.constraintlayout.widget.ConstraintLayout>

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Toolbar.setNavigationIcon(int)' on a null object reference at com.example.khrenovskayastudfarm.HonorsActivity.onCreate(HonorsActivity.java:36)

public class HonorsActivity extends AppCompatActivity {
Toolbar toolbar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_honors);

    toolbar.setNavigationIcon(R.drawable.ic_menu_book);
    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            onBackPressed();
        }
    });

}
}