fix(serializer): incorrect id check

Author: alltouch

lib/serializer.js

@@ -283,7 +283,7 @@ function parseRelations (data, relations, options) {
  * @return {Object|null}
  */
 function makeRelation (type, id, options) {
-  if (_.isEmpty(id)) {
+  if (!_.includes(['string', 'number'], typeof id) || !id) {
     return null
   }