[7.0] AttributeError: 'mgmtsystem.nonconformity' object has no attribute 'message_append'

On 7.0, I created a nonconformity, filled in all the required fields and saved it.

When I clicked on "Send for analysis" button, I got:

Server Traceback (most recent call last):
  File "/home/max/openerp/web/7.0/addons/web/session.py", line 90, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/home/max/openerp/server/7.0/openerp/netsvc.py", line 293, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/home/max/openerp/server/7.0/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/home/max/openerp/server/7.0/openerp/osv/osv.py", line 131, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/max/openerp/server/7.0/openerp/osv/osv.py", line 220, in exec_workflow
    res = self.exec_workflow_cr(cr, uid, obj, signal, *args)
  File "/home/max/openerp/server/7.0/openerp/osv/osv.py", line 213, in exec_workflow_cr
    return object._workflow_signal(cr, uid, [res_id], signal)[res_id]
  File "/home/max/openerp/server/7.0/openerp/osv/orm.py", line 3926, in _workflow_signal
    result[res_id] = wf_service.trg_validate(uid, self._name, res_id, signal, cr)
  File "/home/max/openerp/server/7.0/openerp/workflow/wkf_service.py", line 119, in trg_validate
    res2 = instance.validate(cr, id, ident, signal)
  File "/home/max/openerp/server/7.0/openerp/workflow/instance.py", line 43, in validate
    workitem.process(cr, witem, ident, signal, force_running, stack=stack)
  File "/home/max/openerp/server/7.0/openerp/workflow/workitem.py", line 60, in process
    ok = _split_test(cr, workitem, activity['split_mode'], ident, signal, stack)
  File "/home/max/openerp/server/7.0/openerp/workflow/workitem.py", line 175, in _split_test
    _join_test(cr, t[0], t[1], ident, stack)
  File "/home/max/openerp/server/7.0/openerp/workflow/workitem.py", line 183, in _join_test
    create(cr,[activity], inst_id, ident, stack)
  File "/home/max/openerp/server/7.0/openerp/workflow/workitem.py", line 40, in create
    process(cr, res, ident, stack=stack)
  File "/home/max/openerp/server/7.0/openerp/workflow/workitem.py", line 52, in process
    result = _execute(cr, workitem, activity, ident, stack)
  File "/home/max/openerp/server/7.0/openerp/workflow/workitem.py", line 106, in _execute
    returned_action = wkf_expr.execute(cr, ident, workitem, activity)
  File "/home/max/openerp/server/7.0/openerp/workflow/wkf_expr.py", line 67, in execute
    return _eval_expr(cr, ident, workitem, activity['action'])
  File "/home/max/openerp/server/7.0/openerp/workflow/wkf_expr.py", line 57, in _eval_expr
    ret = eval(line, env, nocopy=True)
  File "/home/max/openerp/server/7.0/openerp/tools/safe_eval.py", line 241, in safe_eval
    return eval(test_expr(expr, _SAFE_OPCODES, mode=mode), globals_dict, locals_dict)
  File "", line 1, in <module>
  File "/home/max/openerp/server/7.0/openerp/osv/orm.py", line 374, in function_proxy
    return attr(self._cr, self._uid, [self._id], *args, **kwargs)
  File "/home/max/openerp/mgmtsystem/7.0/mgmtsystem_nonconformity/mgmtsystem_nonconformity.py", line 200, in wkf_analysis
    self.message_append(cr, uid, self.browse(cr, uid, ids), _('Analysis'))
AttributeError: 'mgmtsystem.nonconformity' object has no attribute 'message_append'