user-list.jsx

export class PopulatedUserList extends Component {

    render() {
        return (
            <div>
                <UserList>{
                    ({users}) => {
                        return <ul>
                            {users.map((user, index) => <li key={index}>{user.id}: {user.name} {user.surname}</li>)}
                        </ul>
                    }
                }
                </UserList>
            </div>
        );
    }

}

Didn't you forget to add the 'fetchUsers' and 'saveUsers' functions in the UserList props?