Hi,i'm trying to modify the fleet module of openerp 7 I added a new class: transport.point but i have this error : Integrity Error

The operation cannot be completed, probably due to the following: - deletion: you may be trying to delete a record while other records still reference it - creation/update: a mandatory field is not correctly set

[object with reference: license_plate - license.plate]

even if i didn't linked this class with the fleet.vehicle

file.py

class fleet_vehicle(osv.osv):

_name = 'fleet.vehicle'
_inherit='fleet.vehicle'
_columns = {
  'type':fields.selection([('ci','C.I'), ('fourgon','Fourgon'),('fourgonnette','Fourgonnette'),('minibus','Mini-bus'),('pickup','Pick-up'),('poidslourds','Poids Lourds'),('vfonction','V.fonction')],'Type'),
  'chauffeur': fields.many2one('hr.employee', 'Chauffeur',required=True),
  'name': fields.char('Nom du point', size=50, required=True),
  'amount': fields.float('Montant'),
}

fleet_vehicle()

class transport_point(osv.osv):
_name = 'transport.point'
     _inherit="fleet.vehicle"
_columns = {
    'name': fields.char('Nom du point', size=50, required=True),
    'amount': fields.float('Montant'),
}
_defaults={
    'amount': 0,
}

transport_point()