Fix KeyError 'statement_note'

lacagette_addons/pos_meal_voucher/models/pos_order.py

@@ -70,7 +70,7 @@ class PosOrder(models.Model):
             raise UserError(_('You have to open at least one cashbox.'))
 
         statement_note = ''
-        if data['statement_note'] != '':
+        if 'statement_note' in data:
             statement_note = data['statement_note']
         args.update({
             'statement_id': statement_id,