Some time ago, I've reported the calls with NULL login and email as a bug: http://ez.no/bugs/view/7461.
Some information on how to make your own login handler can be found in the old documentation: http://ez.no/products/ez_publish_cms/documentation/configuration/configuration/login_handler/how_to_make_your_own_handler
You can also take a look at some login handlers in community/contributions/hacks, like http://ez.no/community/contribs/hacks/cookie_user and http://ez.no/community/contribs/hacks/super_user.
