Allow model configuration to be set to nil.

CHANGELOG.rdoc

@@ -5,6 +5,7 @@
 
 * bug fix
   * Do not redirect on invalid authenticate
+  * Allow model configuration to be set to nil
 
 == 0.2.2
 

lib/devise.rb

@@ -38,7 +38,9 @@ module Devise
 
     mod.const_get(:ClassMethods).class_eval <<-METHOD, __FILE__, __LINE__
       def #{accessor}
-        @#{accessor} || if superclass.respond_to?(:#{accessor})
+        if defined?(@#{accessor})
+          @#{accessor}
+        elsif superclass.respond_to?(:#{accessor})
           superclass.#{accessor}
         else
           Devise.#{accessor}