title: NullPointerException in ActionBar.setHomeButtonEnabled
body: <p>Good evening.
  I have <code>android:minSdkVersion="14"
          android:targetSdkVersion="16"</code></p>
  
  <p>And I have a NullPointerException in onCreate method:</p>
  
  <pre><code>public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.tain);
  
      mCollectionPagerAdapter = new CollectionPagerAdapter(
              getSupportFragmentManager());
  
      final ActionBar actionBar = getActionBar();
  
      //Here is the error
      actionBar.setHomeButtonEnabled(false);
  
      actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
  
      mViewPager = (ViewPager) findViewById(R.id.pager);
      mViewPager.setAdapter(mCollectionPagerAdapter);
      mViewPager.setOnPageChangeListener(
              new ViewPager.SimpleOnPageChangeListener() {
                  @Override
                  public void onPageSelected(int position) {
                      actionBar.setSelectedNavigationItem(position);
                  }
              });
  
          for (int i = 0; i &lt; mCollectionPagerAdapter.getCount(); i++) {
              actionBar.addTab(actionBar.newTab()
                      .setText(mCollectionPagerAdapter.getPageTitle(i))
                      .setTabListener(this));
          }
  
  }
  </code></pre>
  
  <p>I have a simillar code in other project and it works right. The versions of the libraries in both projects are simillar too. What may caused this exception and what can I change?</p>
  
  <p>Thanks. </p>