Replace unless else with if else and fix undefined method error

app/models/ability.rb

@@ -45,14 +45,20 @@ class Ability
     # can view Commercials of confirmed Events
     can :show, Commercial, commercialable_type: 'Event', commercialable_id: Event.where(state: 'confirmed').pluck(:id)
     can [:show, :create], User
-    unless ENV['OSEM_ICHAIN_ENABLED'] == 'true'
+    if ENV['OSEM_ICHAIN_ENABLED'] == 'true'
+      can [:new, :create], Registration do |registration|
+        conference = registration.conference
+        can_register?(conference, registration)
+      end
+
+    else
       can :show, Registration do |registration|
         registration.new_record?
       end
 
       can [:new, :create], Registration do |registration|
         conference = registration.conference
-        can_register?(conference)
+        can_register?(conference, registration)
       end
 
       can :show, Event do |event|
@@ -63,11 +69,6 @@ class Ability
         event.program.cfp_open? && event.new_record?
       end
 
-    else
-      can [:new, :create], Registration do |registration|
-        conference = registration.conference
-        can_register?(conference)
-      end
     end
   end
 
@@ -244,7 +245,7 @@ class Ability
   end
 end
 
-def can_register? conference
+def can_register? conference, registration
   conference.registration_open? &&
   registration.new_record? &&
   !conference.registration_limit_exceeded?