Hi every body ! i tray to programme a calandar view after a click on i have this erreur ??

Traceback (most recent call last):
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/addons/web/http.py", line 341, in dispatch
    response["result"] = self._call_function(**self.params)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/addons/web/http.py", line 210, in _call_function
    return self.func(*args, **kwargs)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/addons/web/http.py", line 1103, in nfunc
    return func(*args, **kwargs)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/addons/web/controllers/main.py", line 1016, in search_read
    return self.do_search_read(model, fields, offset, limit, domain, sort)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/addons/web/controllers/main.py", line 1037, in do_search_read
    request.context)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/addons/web/http.py", line 618, in proxy
    result = meth(cr, request.uid, *args, **kw)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/osv/orm.py", line 2355, in search
    return self._search(cr, user, args, offset=offset, limit=limit, order=order, context=context, count=count)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/osv/orm.py", line 4875, in _search
    query = self._where_calc(cr, user, args, context=context)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/osv/orm.py", line 4704, in _where_calc
    e = expression.expression(cr, user, domain, self, context)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/osv/expression.py", line 639, in __init__
    self.parse(cr, uid, context=context)
  File "/home/mlouk/workspace/workspace/madrassa_local/openerp/osv/expression.py", line 756, in parse
    field_path = left.split('.', 1)
AttributeError: 'NoneType' object has no attribute 'split'