Agenda keeps stopping. O app nao abre mais!

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/activity_main_fab_novo_aluno"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:layout_margin="16dp"
        android:clickable="true"
        android:focusable="true" />

    <ListView
        android:id="@+id/activity_main_lista_de_alunos"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

MainActivity.java

package alura.com.agenda;

import android.app.Activity; import android.os.Bundle; import android.widget.ArrayAdapter; import android.widget.ListView; import androidx.annotation.Nullable; import java.util.ArrayList; import java.util.Arrays; import java.util.List;

public class MainActivity extends Activity {

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    List<String> alunos = new ArrayList<>(
            Arrays.asList("Alex", "Fran", "Jose", "Maria", "Ana"));
    ListView listaDeAlunos = findViewById(R.id.activity_main_lista_de_alunos);
    listaDeAlunos.setAdapter(new ArrayAdapter<>(
            this,
            android.R.layout.simple_list_item_1,
            alunos));
}

}

AndroidManifest.xml

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="Agenda"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity>
</application>