pointerToId = function pointerToId(object) {
        if (object instanceof AV.Object) {
          if (!object.id) {
            throw "You can't add an unsaved AV.Object to a relation.";
          }
          if (!self._targetClassName) {
            self._targetClassName = object.className;
          }
          if (self._targetClassName !== object.className) {
            throw "Tried to create a AV.Relation with 2 different types: " + self._targetClassName + " and " + object.className + ".";
          }
          return object.id;
        }
        return object;
      }
Returns an array of unfetched AV.Object that are being added to the
relation.
@return {Array}