Activity dialog with tab

I am building application for tab.

1. On click of button I am trying to show Activity (say A) with theme @android:style/Theme.Dialog
2. Inside activity A I am creating actionbar and adding 4 tabs.
3. On click of tab I want to change fragment.

Everything works fine until I am not applying theme @android:style/Theme.Dialog After applying theme I am getting exception:

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ebuilder/com.ebuilder.views.MyTabActivity}: java.lang.NullPointerException

at following line:

actionBar.addTab(actionBar.newTab().setCustomView(R.layout.tab_home).
                    setTabListener(homeListener), 0);

I have two questions:

1. What is going wrong if I apply theme dialog?

2. Is my approach right?

Let me know if anybody know another approach.

Edit1: *Manifest file*

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.vivek"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk  android:targetSdkVersion="14"/>

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".FragmentInsideFragmentTestActivity"
            android:label="@string/app_name"
            android:theme="@style/Theme.CustomDialog" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

res/values/style.