Serialize associations that doesn't have an associated serializer

lib/active_model/array_serializer.rb

@@ -1,3 +1,4 @@
+require 'active_model/default_serializer'
 require 'active_model/serializable'
 require 'active_model/serializer'
 
@@ -22,12 +23,8 @@ module ActiveModel
 
     def serializable_array
       @object.map do |item|
-        serializer = @options[:each_serializer] || Serializer.serializer_for(item)
-        if serializer
-          serializer.new(item).serializable_object(@options.merge(root: nil))
-        else
-          item.as_json
-        end
+        serializer = @options[:each_serializer] || Serializer.serializer_for(item) || DefaultSerializer
+        serializer.new(item).serializable_object(@options.merge(root: nil))
       end
     end
     alias serializable_object serializable_array

lib/active_model/default_serializer.rb

@@ -0,0 +1,17 @@
+module ActiveModel
+  # DefaultSerializer
+  #
+  # Provides a constant interface for all items
+  class DefaultSerializer
+    attr_reader :object
+
+    def initialize(object, options=nil)
+      @object = object
+    end
+
+    def serializable_hash(*)
+      @object.as_json
+    end
+    alias serializable_object serializable_hash
+  end
+end

lib/active_model/serializer/associations.rb

@@ -1,3 +1,4 @@
+require 'active_model/default_serializer'
 require 'active_model/serializer'
 
 module ActiveModel
@@ -32,13 +33,8 @@ module ActiveModel
       end
 
       def build_serializer(object)
-        @serializer_class ||= Serializer.serializer_for(object)
-
-        if @serializer_class
-          @serializer_class.new(object, @options)
-        else
-          object
-        end
+        @serializer_class ||= Serializer.serializer_for(object) || DefaultSerializer
+        @serializer_class.new(object, @options)
       end
 
       class HasOne < Association