<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def group_members(self, group):
 """Return a hash or users with their information. Requires JIRA 6.0 or will raise NotImplemented. :param group: Name of the group. :type group: str """

        if self._version < (6, 0, 0):
            raise NotImplementedError(
                "Group members is not implemented in JIRA before version 6.0, upgrade the instance, if possible.")

        params = {'groupname': group, 'expand': "users"}
        r = self._get_json('group', params=params)
        size = r['users']['size']
        end_index = r['users']['end-index']

        while end_index < size - 1:
            params = {'groupname': group, 'expand': "users[%s:%s]" % (
                end_index + 1, end_index + 50)}
            r2 = self._get_json('group', params=params)
            for user in r2['users']['items']:
                r['users']['items'].append(user)
            end_index = r2['users']['end-index']
            size = r['users']['size']

        result = {}
        for user in r['users']['items']:
            result[user['key']] = {'name': user['name'],
                                   'fullname': user['displayName'],
                                   'email': user.get('emailAddress', 'hidden'),
                                   'active': user['active']}
        return OrderedDict(sorted(result.items(), key=lambda t: t[0]))