Android : How to get the Action Bar to display an icon and no title in both states of Navigation drawer?

I am trying to get my Action Bar to display an icon and not display any title while both states of the Navigation Drawer (open and closed) I read the documentation on developers android about how to modify the contents of the Action Bar when the drawer is visible. As the page said, I created an instance of ActionBarDrawerToggle and set the icon and set title to null. But still I am not able to see any icon and the app title appears as soon as I draw out the Navigation drawer. The following is the code I have used in onCreate of my activity

 mToggle = new ActionBarDrawerToggle(
            this,
            drawerLayout,
            R.string.drawer_open_or_close,
            R.string.drawer_open_or_close) {

        /** Called when a drawer has settled in a completely closed state. */
        public void onDrawerClosed(View view) {
            super.onDrawerClosed(view);
            getActionBar().setTitle(R.string.drawer_open_or_close);
            getActionBar().setIcon(R.drawable.icon_144);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }

        /** Called when a drawer has settled in a completely open state. */
        public void onDrawerOpened(View drawerView) {
            super.onDrawerOpened(drawerView);
            getActionBar().setTitle(R.string.drawer_open_or_close);
            getActionBar().setIcon(R.drawable.icon_144);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }
    };

As you can see, I have set the Action bar title to R.string.drawer_open_or_close, which is an empty string, during both completely open and completely closed state. I have set the app icon in both cases as well. What am I missing here?

Edit: I had forgotten to set the drawer toggle as DrawerListener, which I did

drawerLayout.setDrawerListener(mToggle);

Now when I open Navigation drawer, the app force closes and the log cat says java.lang.NullPointerException at

getActionBar().setTitle(R.string.drawer_open_or_close);