message: Fix exception on logout
  Don't try to unregister if we never registered
diff: @@ -46,6 +46,8 @@ export default class EmbeddedPage extends React.PureComponent {
  constructor(props) {
  super(props);
  + this._dispatcherRef = null;
  +
  this.state = {
  page: '',
  };
  @@ -90,7 +92,7 @@ export default class EmbeddedPage extends React.PureComponent {
  componentWillUnmount() {
  this._unmounted = true;
  - dis.unregister(this._dispatcherRef);
  + if (this._dispatcherRef !== null) dis.unregister(this._dispatcherRef);
  }
  onAction = (payload) => {
  