Button Onclick works with api 25 but fails with api 18 - Android Studio

Question

It fails on the intent = new intent() line. Please help me thanks.

Intent intent;

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

}

public void buttonTapped(View view){
    int id = view.getId();
    String ourId = "";
    ourId = view.getResources().getResourceEntryName((id));

    intent = new Intent(getApplicationContext(), aboutUsActivity.class);
    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    getApplicationContext().startActivity(intent);

    //Log.i("button tapped", ourId);
}

E/AndroidRuntime: FATAL EXCEPTION: main java.lang.IllegalStateException: Could not execute method for android:onClick at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293) at android.view.View.performClick(View.java:4240) at android.view.View$PerformClick.run(View.java:17721) at android.os.Handler.handleCallback(Handler.java:730) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:5103) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) at android.view.View.performClick(View.java:4240)  at android.view.View$PerformClick.run(View.java:17721)  at android.os.Handler.handleCallback(Handler.java:730)  at android.os.Handler.dispatchMessage(Handler.java:92)  at android.os.Looper.loop(Looper.java:137)  at android.app.ActivityThread.main(ActivityThread.java:5103)  at java.lang.reflect.Method.invokeNative(Native Method)  at java.lang.reflect.Method.invoke(Method.java:525)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)  at dalvik.system.NativeStart.main(Native Method)  Caused by: java.lang.NullPointerException at com.kshakoor.iiql.MainActivity.buttonTapped(MainActivity.java:68) at java.lang.reflect.Method.invokeNative(Native Method)  at java.lang.reflect.Method.invoke(Method.java:525)  at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)  at android.view.View.performClick(View.java:4240)  at android.view.View$PerformClick.run(View.java:17721)  at android.os.Handler.handleCallback(Handler.java:730)  at android.os.Handler.dispatchMessage(Handler.java:92)  at android.os.Looper.loop(Looper.java:137)  at android.app.ActivityThread.main(ActivityThread.java:5103)  at java.lang.reflect.Method.invokeNative(Native Method)  at java.lang.reflect.Method.invoke(Method.java:525)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)  at dalvik.system.NativeStart.main(Native Method) 

Application terminated.