message: Fall back to MXID when no display name is present
  MemberAvatar requires a display name, or else it refuses to render.
diff: @@ -101,7 +101,7 @@ export default class EventTilePreview extends React.Component<IProps, IState> {
  // Fake it more
  event.sender = {
  - name: this.props.displayName,
  + name: this.props.displayName || this.props.userId,
  userId: this.props.userId,
  getAvatarUrl: (..._) => {
  return Avatar.avatarUrlForUser(
  