Wizard "Annotations by classe" crashes when add a new annotation.

Error report:
Server Traceback (most recent call last):
  File "/opt/openerp/server/openerp/addons/web/common/http.py", line 593, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/opt/openerp/server/openerp/netsvc.py", line 360, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/opt/openerp/server/openerp/service/web_services.py", line 586, in dispatch
    res = fn(db, uid, *params)
  File "/opt/openerp/server/openerp/osv/osv.py", line 167, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/opt/openerp/server/openerp/osv/osv.py", line 121, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/opt/openerp/server/openerp/osv/osv.py", line 176, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/opt/openerp/server/openerp/osv/osv.py", line 164, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/opt/openerp/server/openerp/addons/school_attendance/wizards/school_annotations_by_classe.py", line 257, in write
    self.datas[wiz_id][key] = value
AttributeError: 'school_annotations_by_classe' object has no attribute 'datas'