Merge pull request matrix-org#1054 from rcsm/develop

Properly document the function possible returns for getRelationsForEvent

src/models/event-timeline-set.js

@@ -695,9 +695,12 @@ EventTimelineSet.prototype.compareEventOrdering = function(eventId1, eventId2) {
  * The type of relation involved, such as "m.annotation", "m.reference", "m.replace", etc.
  * @param {String} eventType
  * The relation event's type, such as "m.reaction", etc.
+ * @throws If <code>eventId</code>, <code>relationType</code> or <code>eventType</code>
+ * are not valid.
  *
- * @returns {Relations}
- * A container for relation events.
+ * @returns {?Relations}
+ * A container for relation events or undefined if there are no relation events for
+ * the relationType.
  */
 EventTimelineSet.prototype.getRelationsForEvent = function(
     eventId, relationType, eventType,