Returns the previous url.

def get_redirect(self):
        """
            Returns the previous url.
        """
        index_url = self.appbuilder.get_url_for_index
        page_history = Stack(session.get("page_history", []))

        if page_history.pop() is None:
            return index_url
        session["page_history"] = page_history.to_json()
        url = page_history.pop() or index_url
        return url