when user selects anyother value rather than nil i want to make form readonly so i used this but it is not working if anyone have idea please help me here is my code <sheet readonly="state !='nil'">
<field name="state"/>
python code: state = fields.Selection([
('nil', 'Nil'),
('open', 'open'),
('in_progress', 'In Progress'),
('resolved', 'Resolved'),
('closed', 'Closed')
], string="Status", default="nil")