code: function(data, payload) {
          var type = data.length > 0 ? data[0].type : null;
          var serializer = this;
          data.forEach(function(item) {
            if(item.relationships) {
              serializer.extractRelationships(item.relationships, item);
            }
          });
  
          payload[type] = data;
        }
docs: Extract top-level "data" containing a single primary data