PreferenceActivity -> getActionBar().setDisplayHomeAsUpEnabled giving NullPointerException - android-activity

Question

I have some questions about a discussed topic.
I get a NullPointerException from the following code. My questions are:
Why do I get a NullPointerException ? i.e. why does getActionBar() return null ?
Request answers to be in Layman terms please.
SettingActivity.java
public class SettingsActivity extends PreferenceActivity {
/**
* Determines whether to always show the simplified settings UI, where
* settings are presented in a single list. When false, settings are shown
* as a master/detail two-pane view on tablets. When true, a single pane is
* shown on tablets.
*/
private static final boolean ALWAYS_SIMPLE_PREFS = false;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setupActionBar();
}
/**
* Set up the {#link android.app.ActionBar}, if the API is available.
*/
#TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void setupActionBar() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
// Show the Up button in the action bar.
getSupportActionBar()
getActionBar().setDisplayHomeAsUpEnabled(true);
}
}
Style.xml
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- Customize your theme here. -->
</style>
build.gradle
dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
compile 'com.android.support:appcompat-v7:22.1.1'
compile 'com.android.support:support-v4:22.1.1'
}
Error
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
at com.example.deep.sunshine.SettingsActivity.setupActionBar(SettingsActivity.java:59)
at com.example.deep.sunshine.SettingsActivity.onCreate(SettingsActivity.java:49)