Using Fragment, Error in Activity

I'm creating an app and would like to know where I'm going wrong, it's working, but in the error fragment activity.

package com.example.ronysueliton.patospizzas;

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.util.Log;


public class Nome_Pizzaria extends FragmentActivity {

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

    ActionBar ab = getActionBar();
    ab.setDisplayHomeAsUpEnabled(true);
    ab.setBackgroundDrawable(getResources().getDrawable(R.drawable.logo));

    //TABS

    ab.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    ActionBar.Tab tab1 = ab.newTab();
    tab1.setText("Pizzas");
    tab1.setTabListener(new NavegacaoTabs(new Fragment1()));
    ab.addTab(tab1);

    ActionBar.Tab tab2 = ab.newTab();
    tab2.setText("Favoritos");
    tab2.setTabListener(new NavegacaoTabs(new Fragment2()));
    ab.addTab(tab2);

}

private class NavegacaoTabs implements ActionBar.TabListener{

    private Fragment frag;

    public NavegacaoTabs(Fragment frag){
        this.frag=frag;
    }


    @Override
    public void onTabReselected(ActionBar.Tab tab, android.app.FragmentTransaction ft) {
        Log.i("Script", "onTabReSelected(0");

    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, android.app.FragmentTransaction ft) {
        FragmentTransaction fts = getSupportFragmentManager().beginTransaction();
        fts.replace(R.id.fragmentContainer, frag);
        fts.commit();

    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, android.app.FragmentTransaction ft) {
        FragmentTransaction fts = getSupportFragmentManager().beginTransaction();
        fts.remove(frag);
        fts.commit();
    }
}

}

LOGCAT

04-11 12:39:04.186  16835-16835/com.example.ronysueliton.patospizzas D/AndroidRuntime﹕ Shutting down VM
04-11 12:39:04.205  16835-16835/com.example.ronysueliton.patospizzas E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.ronysueliton.patospizzas, PID: 16835
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ronysueliton.patospizzas/com.example.ronysueliton.patospizzas.Nome_Pizzaria}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
            at android.app.ActivityThread.access$800(ActivityThread.java:148)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5312)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at com.example.ronysueliton.patospizzas.Nome_Pizzaria.onCreate(Nome_Pizzaria.java:22)
            at android.app.Activity.performCreate(Activity.java:5953)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1128)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
            at android.app.ActivityThread.access$800(ActivityThread.java:148)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5312)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

No ActionBar