docs: function(snapshot, json, relationship) {
      var key = relationship.key;
      var belongsTo = snapshot.belongsTo(key);
      var jsonKey = underscore(key + "_type");
  
      if (Ember.isNone(belongsTo)) {
        json[jsonKey] = null;
      } else {
        json[jsonKey] = classify(belongsTo.modelName).replace('/', '::');
      }
    }