Implement a NullAdapter.

This adapter basically doesn't do anything, and just serializes
the attributes into plain old JSON.

lib/active_model/serializer.rb

@@ -10,6 +10,13 @@ module ActiveModel
 
     def self.attributes(*attrs)
       @_attributes.concat attrs
+
+      
+      attrs.each do |attr|
+        define_method attr do
+          object.read_attribute_for_serialization(attr)
+        end unless method_defined?(attr)
+      end
     end
 
     attr_accessor :object
@@ -17,5 +24,11 @@ module ActiveModel
     def initialize(object)
       @object = object
     end
+
+    def attributes
+      self.class._attributes.dup.each_with_object({}) do |name, hash|
+        hash[name] = send(name)
+      end
+    end
   end
 end

lib/active_model/serializer/adapter/null_adapter.rb

@@ -0,0 +1,17 @@
+module ActiveModel
+  class Serializer
+    class Adapter
+      class NullAdapter
+        def initialize(serializer)
+          @serializer = serializer
+        end
+
+        def to_json
+          @serializer.attributes.each_with_object({}) do |(attr, value), h|
+            h[attr] = value
+          end.to_json
+        end
+      end
+    end
+  end
+end