Fix relationshipLinks on nested relationship

Author: Vincent Molinié

lib/serializer-utils.js

@@ -191,6 +191,13 @@ module.exports = function (collectionName, record, payload, opts) {
     var includedAttrs = [];
 
     if (opts.attributes) {
+      if (dest) {
+        opts.attributes.forEach(function (attr) {
+          if (opts[attr] && !dest[attr] && opts[attr].nullIfMissing) {
+            dest[attr] = null;
+          }
+        });
+      }
       relationships = opts.attributes.filter(function (attr) {
         return opts[attr];
       });
@@ -204,7 +211,7 @@ module.exports = function (collectionName, record, payload, opts) {
     if (includedAttrs) { included.attributes = pick(dest, includedAttrs); }
 
     relationships.forEach(function (relationship) {
-      if (dest && isComplexType(dest[relationship])) {
+      if (dest && (isComplexType(dest[relationship]) || dest[relationship] === null)) {
         that.serialize(included, dest, relationship, opts[relationship]);
       }
     });