Implement a NullAdapter.

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

test/fixtures/poro.rb

@@ -2,6 +2,14 @@ class Model
   def initialize(hash={})
     @attributes = hash
   end
+
+  def read_attribute_for_serialization(name)
+    if name == :id || name == 'id'
+      object_id
+    else
+      @attributes[name]
+    end
+  end
 end
 
 class Profile < Model