Merge pull request #657 from Zooip/fix_nil_data_on_polymorphic_to_one_relationship

Accept nil data when updating polymorphic to_one relationship

Author: lgebhardt

lib/jsonapi/request.rb

@@ -585,8 +585,8 @@ def parse_update_relationship_operation(verified_params, relationship, parent_ke
       if relationship.is_a?(JSONAPI::Relationship::ToOne)
         if relationship.polymorphic?
           operation_args[1].merge!(
-            key_value: verified_params[:to_one].values[0][:id],
-            key_type: verified_params[:to_one].values[0][:type]
+            key_value: verified_params[:to_one].values[0] && verified_params[:to_one].values[0][:id],
+            key_type: verified_params[:to_one].values[0] && verified_params[:to_one].values[0][:type]
           )
 
           operation_klass = JSONAPI::ReplacePolymorphicToOneRelationshipOperation