Allow for nil user class if user model exists

lib/blazer/engine.rb

@@ -11,7 +11,7 @@ module Blazer
       Blazer.user_name = Blazer.settings["user_name"] if Blazer.settings["user_name"]
       Blazer.from_email = Blazer.settings["from_email"] if Blazer.settings["from_email"]
 
-      Blazer.user_class ||= Blazer.settings["user_class"] || User rescue nil
+      Blazer.user_class ||= Blazer.settings.key?("user_class") ? Blazer.settings["user_class"] : (User rescue nil)
       Blazer.user_method = Blazer.settings["user_method"]
       if Blazer.user_class
         Blazer.user_method ||= "current_#{Blazer.user_class.to_s.downcase.singularize}"