<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_users(self, course):
 """ Returns a sorted list of users """

        users = OrderedDict(sorted(list(self.user_manager.get_users_info(self.user_manager.get_course_registered_users(course)).items()),
            key=lambda k: k[1][0] if k[1] is not None else ""))
        return users