message: Simplified check because link can't be ''
diff: @@ -10,9 +10,7 @@ class HTML5HistoryManager implements HistoryManager {
  }
  init(navigateHistory: (url?: string) => void) {
  - this.navigateHistory = e => {
  - navigateHistory(e.state != null ? e.state : undefined);
  - };
  + this.navigateHistory = e => navigateHistory(e.state || undefined);
  if (!this.disabled) {
  window.addEventListener('popstate', this.navigateHistory);
  }
  