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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def read_preferences_file(self):
 """ If json preferences file exists, read it in. """

        user_data_dir = find_pmag_dir.find_user_data_dir("thellier_gui")
        if not user_data_dir:
            return {}
        if os.path.exists(user_data_dir):
            pref_file = os.path.join(user_data_dir, "thellier_gui_preferences.json")
            if os.path.exists(pref_file):
                with open(pref_file, "r") as pfile:
                    return json.load(pfile)
        return {}