i redefined copy_data function in my class, when i want to get nContrat value from the object and increment it after duplicated it, my code give me an error, can someone have any idea how to slove it ??

def copy_data(self, cr, uid, id, default=None, context=None): if default is None: default = {}

res = 1                                              <---------------------
res += default.get('nContrat')                       <---------------------
default['nContrat'] = res                            <---------------------

return super(io_assurance, self).copy_data( cr, uid, id, default=res, context=context)

when i use my code i get this error ( TypeError: unsupported operand type(s) for +=: 'int' and 'NoneType' ) anyone havy any idea how to slove this problem ???