Throw an exception if isValidFragment is not overridden for KK targets

     */

    protected boolean isValidFragment(String fragmentName) {

        if (getApplicationInfo().targetSdkVersion  >= android.os.Build.VERSION_CODES.KITKAT) {

            Log.w(TAG, "Subclasses of PreferenceActivity must override isValidFragment(String)"

            throw new RuntimeException(

                    "Subclasses of PreferenceActivity must override isValidFragment(String)"

                    + " to verify that the Fragment class is valid! " + this.getClass().getName()

                    + " has not checked if fragment " + fragmentName + " is valid.");

            // Return true for now, but will eventually return false when all bundled apps

            // have been modified. TODO: change to return false

            return true;

        } else {

            Log.i(TAG, "PreferenceActivity built on pre-KLP launching fragment: " + fragmentName);

            return true;

        }

    }