Support serializers with no attributes.

Author: fotinakis

lib/jsonapi-serializers/serializer.rb

@@ -139,6 +139,7 @@ def relationships
       end
 
       def attributes
+        return {} if self.class.attributes_map.nil?
         attributes = {}
         self.class.attributes_map.each do |attribute_name, attr_data|
           next if !should_include_attr?(attr_data[:options][:if], attr_data[:options][:unless])

spec/serializer_spec.rb

@@ -275,6 +275,18 @@ def serialize_primary(object, options = {})
         })
       end
     end
+    it 'can serialize primary data for an empty serializer with no attributes' do
+      post = create(:post)
+      primary_data = serialize_primary(post, {serializer: MyApp::EmptySerializer})
+      expect(primary_data).to eq({
+        'id' => '1',
+        'type' => 'posts',
+        'attributes' => {},
+        'links' => {
+          'self' => '/posts/1',
+        },
+      })
+    end
   end
 
   describe 'JSONAPI::Serializer.serialize' do

spec/support/serializers.rb

@@ -95,4 +95,8 @@ def hide_body?
       context.fetch(:hide_body, false)
     end
   end
+
+  class EmptySerializer
+    include JSONAPI::Serializer
+  end
 end