Correct handling for to-one nil relationships.

Author: fotinakis

lib/jsonapi/resource_serializer.rb

@@ -110,6 +110,8 @@ def process_primary(source, requested_associations)
           add_included_object(@primary_class_name, id, object_hash(resource,  requested_associations), true)
         end
       else
+        return {} if source.nil?
+
         resource = source
         id = resource.id
         # ToDo: See if this is actually needed

test/unit/serializer/serializer_test.rb

@@ -57,6 +57,15 @@ def test_serializer
     )
   end
 
+  def test_serializer_nil_handling
+    assert_hash_equals(
+      {
+        data: nil
+      },
+      JSONAPI::ResourceSerializer.new(PostResource).serialize_to_hash(nil)
+    )
+  end
+
   def test_serializer_namespaced_resource
     assert_hash_equals(
       {