code: protected final void notifyError(@NonNull final Throwable e) {
          //noinspection ThrowableResultOfMethodCallIgnored
          checkNotNull(e, "e");
          runOnUiThread(new Runnable() {
              @Override
              public void run() {
                  mErrorObservable.notifyError(e);
              }
          });
      }
docs: Dispatch an error notification on the UI thread.