[FIX] Override the field to add the value instead of breaking the validation system

report_xls/ir_report.py

@@ -20,15 +20,10 @@
 #
 ##############################################################################
 
-from openerp import models
+from openerp import models, fields
 
 
 class IrActionsReportXml(models.Model):
     _inherit = 'ir.actions.report.xml'
 
-    def _check_selection_field_value(self, cr, uid,
-                                     field, value, context=None):
-        if field == 'report_type' and value == 'xls':
-            return
-        return super(IrActionsReportXml, self)._check_selection_field_value(
-            cr, uid, field, value, context=context)
+    report_type = fields.Selection(selection_add=[('xls', 'XLS')])