Update utils to fix Deskpro empty user_email error
Update utils to fix Deskpro empty user_email error

Deskpro user_email will now use the default address from the app
configuration if `user_email` argument was set to an empty string.

gov-cjwaszczuk/notifications-admin,alphagov/notifications-admin,gov-cjwaszczuk/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,gov-cjwaszczuk/notifications-admin,gov-cjwaszczuk/notifications-admin,alphagov/notifications-admin