[POS] Bug After canceling a Payment

Hello.

1/ Do an order on the POS.

2/ Click a Payment mode.

3/ In the payment widget, Cancel the payment (with the cross on the right of the payment)

.../... Then, when there's no more line of payment

4/ Click on the Backspace or on a digit in the virtual numpad, you'll get an error.

Uncaught TypeError: Cannot call method 'set_amount' of undefined
https://demo2.openerp.com/web/webclient/js?mods=web_diagram%2Cbase%2Cbase_setup%2Cprocess%2Cmail%2Cemail_template%2Cbase_calendar%2Cboard%2Ccrm%2Cproject%2Cproject_issue%2Cshare%2Cauth_signup%2Cportal%2Cportal_project_issue%2Chr%2Cportal_crm%2Cportal_hr_employees%2Chr_attendance%2Cweb_graph%2Cedi%2Caccount%2Caccount_voucher%2Caccount_accountant%2Csale%2Caccount_analytic_analysis%2Caccount_asset%2Cfleet%2Chr_expense%2Chr_holidays%2Csurvey%2Chr_recruitment%2Chr_timesheet_sheet%2Clunch%2Cstock%2Cpurchase%2Cmrp%2Cnote%2Cpad%2Cpoint_of_sale%2Cweb_analytics%2Csaas_demo%2Cweb_view_editor%2Cweb_calendar%2Cweb_tests%2Cweb_gantt:1386
Ok

I think that Numpad should be desactived when there is no more payment line, or, the delete of the last payment should execute an exit of the payment Widget.

Sorry for my english.

thank you.