state field is missing :(

I cant find state in columns of expenses line
class hr_expense_line(osv.osv):
    _name = "hr.expense.line"
    _description = "Expense Line"
    def _amount(self, cr, uid, ids, field_name, arg, context):
        if not len(ids):
            return {}
        id_set = ",".join(map(str, ids))
        cr.execute("SELECT l.id,COALESCE(SUM(l.unit_amount*l.unit_quantity),0) AS amount FROM hr_expense_line l WHERE id IN ("+id_set+") GROUP BY l.id ")
        res = dict(cr.fetchall())
        return res

    _columns = {
        'name': fields.char('Short Description', size=128, required=True),
        'date_value': fields.date('Date', required=True),
        'expense_id': fields.many2one('hr.expense.expense', 'Expense', ondelete='cascade', select=True),
        'total_amount': fields.function(_amount, method=True, string='Total'),
        'unit_amount': fields.float('Unit Price', readonly=True, states={'draft':[('readonly',False)]}),
        'unit_quantity': fields.float('Quantities', readonly=True, states={'draft':[('readonly',False)]}),
        'product_id': fields.many2one('product.product', 'Product', readonly=True, states={'draft':[('readonly',False)]}),
        'uom_id': fields.many2one('product.uom', 'UoM', readonly=True, states={'draft':[('readonly',False)]}),
        'description': fields.text('Description'),
        'analytic_account': fields.many2one('account.analytic.account','Analytic account'),
        'ref': fields.char('Reference', size=32),
        'sequence' : fields.integer('Sequence'),
    }

in this code
        'product_id': fields.many2one('product.product', 'Product', readonly=True, states={'draft':[('readonly',False)]}),

means i can fill product when state=draft

but i tried my best to find that field in this object but i cant find that. So please help me to find that.

i check in both

http://bazaar.launchpad.net/%7Eopenerp/openobject-addons/5.0/
and
http://bazaar.launchpad.net/%7Eopenerp/openobject-addons/trunk/

so please try to solve that.