Remove nil relationships links (#1833)

Author: Yohan Robert

CHANGELOG.md

@@ -8,6 +8,8 @@ Features:
 
 Fixes:
 
+- [#1833](https://github.com/rails-api/active_model_serializers/pull/1833) Remove relationship links if they are null (@groyoh)
+
 Misc:
 
 ### [v0.10.2 (2016-07-05)](https://github.com/rails-api/active_model_serializers/compare/v0.10.1...v0.10.2)

lib/active_model_serializers/adapter/json_api/relationship.rb

@@ -13,7 +13,8 @@ def initialize(parent_serializer, serializer, serializable_resource_options, arg
           @serializable_resource_options = serializable_resource_options
           @data = data_for(serializer)
           @links = args.fetch(:links, {}).each_with_object({}) do |(key, value), hash|
-            hash[key] = ActiveModelSerializers::Adapter::JsonApi::Link.new(parent_serializer, value).as_json
+            result = Link.new(parent_serializer, value).as_json
+            hash[key] = result if result
           end
           meta = args.fetch(:meta, nil)
           @meta = meta.respond_to?(:call) ? parent_serializer.instance_eval(&meta) : meta

test/adapter/json_api/relationships_test.rb

@@ -13,8 +13,9 @@ class RelationshipAuthorSerializer < ActiveModel::Serializer
             end
 
             has_one :profile do
+              id = object.profile.id
               link :related do
-                "//example.com/profiles/#{object.profile.id}"
+                "//example.com/profiles/#{id}" if id != 123
               end
             end
 
@@ -113,6 +114,14 @@ def test_relationship_block_link
             assert_relationship(:profile, expected)
           end
 
+          def test_relationship_nil_link
+            @author.profile.id = 123
+            expected = {
+              data: { id: '123', type: 'profiles' }
+            }
+            assert_relationship(:profile, expected)
+          end
+
           def test_relationship_block_link_href
             expected = {
               data: [{ id: '1337', type: 'locations' }],