@utilities.arguments_not_none<EOL><INDENT>def change_branch(self, branch_id, proxy):<DEDENT>
raise errors.Unimplemented()<EOL>
Changes the service branch.

        arg:    branch_id (osid.id.Id): the new service branch
        arg:    proxy (osid.proxy.Proxy): a proxy
        raise:  NotFound - ``branch_id`` not found
        raise:  NullArgument - ``branch_id`` or ``proxy`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure occurred
        raise:  Unimplemented - ``supports_journal_branching()`` is
                ``false``
        *compliance: mandatory -- This method must be implemented.*