String set to ArrayList?

So I was looking up how to change a String set to an ArrayList<sSring> and I couldn't find anything. I tried:

favorites  = new ArrayList( mPrefsaved.getStringSet("faves", null) ;

How can I convert a StringSet into an ArrayList<string>?

I tried:

  private void getsaved() {

      favorites = new ArrayList<String>(mPrefsaved.getStringSet("faves", null));

}

But log Cat told me NullPointerException