Executando a primeira vez a lista o app não executa

package viktorrocha.br.com.agenda;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class ListaAlunoActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        String[] alunos = {"Daniel", "Ronaldo", "Karen", "Luiza"};
        ListView listaAlunos =  findViewById(R.id.lista_alunos);
        ArrayAdapter<String> adapter =
                new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, alunos);
        listaAlunos.setAdapter(adapter);
    }
}

Erro

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: viktorrocha.br.com.agenda, PID: 27068
    java.lang.RuntimeException: Unable to start activity ComponentInfo{viktorrocha.br.com.agenda/viktorrocha.br.com.agenda.ListaAlunoActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2319)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2370)
        at android.app.ActivityThread.access$800(ActivityThread.java:155)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1243)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5426)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
        at viktorrocha.br.com.agenda.ListaAlunoActivity.onCreate(ListaAlunoActivity.java:18)
        at android.app.Activity.performCreate(Activity.java:5296)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2283)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2370) 
        at android.app.ActivityThread.access$800(ActivityThread.java:155) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1243) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:136) 
        at android.app.ActivityThread.main(ActivityThread.java:5426) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:515) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084) 
        at dalvik.system.NativeStart.main(Native Method)