diff --git a/addons/mail/models/ir_attachment.py b/addons/mail/models/ir_attachment.py
index 707b7383a0d..1912ea903d1 100644
--- a/addons/mail/models/ir_attachment.py
+++ b/addons/mail/models/ir_attachment.py
@@ -42,7 +42,7 @@ class IrAttachment(models.Model):
         if message:
             message.write({})  # to make sure write_date on the message is updated
         self.env['bus.bus']._sendmany((attachment._bus_notification_target(), 'ir.attachment/delete', {
-            'id': attachment.id, 'message': {'id': message.id, 'write_date': message.write_date} if message else {}
+            'id': attachment.id, 'message': {'id': message.id, 'write_date': message.write_date} if message else None
         }) for attachment in self)
         self.unlink()