Implement a NullAdapter.

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

test/adapters/null_adapter_test.rb

@@ -0,0 +1,24 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class NullAdapterTest < Minitest::Test
+        def setup
+          @profile = Profile.new({ name: 'Name 1', description: 'Description 1', comments: 'Comments 1' })
+          @profile_serializer = ProfileSerializer.new(@profile)
+
+          @adapter = NullAdapter.new(@profile_serializer)
+        end
+
+        def test_null_adapter
+          assert_equal('{"name":"Name 1","description":"Description 1"}',
+                       @adapter.to_json)
+
+JSON
+        end
+      end
+    end
+  end
+end
+

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