Concrete adapter should provide serializable hash for Adapter#to_json method

lib/active_model/serializer/adapter.rb

@@ -15,8 +15,8 @@ module ActiveModel
         raise NotImplementedError, 'This is abstract method. Should be implemented at concrete adapter.'
       end
 
-      def to_json(options = {})
-        raise NotImplementedError, 'This is abstract method. Should be implemented at concrete adapter.'
+      def to_json(options={})
+        serializable_hash(options).to_json
       end
 
       def self.adapter_for(serializer)

lib/active_model/serializer/adapter/null_adapter.rb

@@ -5,10 +5,6 @@ module ActiveModel
         def serializable_hash(options = {})
           {}
         end
-
-        def to_json(options = {})
-          serializable_hash.to_json
-        end
       end
     end
   end

lib/active_model/serializer/adapter/simple_adapter.rb

@@ -7,10 +7,6 @@ module ActiveModel
             h[attr] = value
           end
         end
-
-        def to_json(options={})
-          serializable_hash(options).to_json
-        end
       end
     end
   end