fixed to set creation_user only if party_from is actually a user. fixed to use the acs-kernel param OutgoingSender if party_from doesn't have an email address.
fixed a problem where I was sending party_from as creation_user. But some packages use party_from as addresses which are not 'users' and putting those parties in as creation_user then violates the FK requirement in acs_objects->users. So, I've made the creation_user 'null' for now