Before this commit when you create an event from a lead, a button appears to jump back to the lead but while you're creating the record, it already appears but empty. This commit hides the button in case the res_model_name is null, which happens while we are creating the event and before hitting save. closes odoo/odoo#154956 Task: 3747059 Signed-off-by: Arnaud Joset (arj) <arj@odoo.com>