What means this error, pray tell.

0100-var-log-apache2-my_site-error.log

I have a fresh rebuild of my site, with a restoration of the production website; 
its comes up without issue.  

I run `drush cr` 

and harvest a one-time login with `drush uli`

when I use that link to log in, I am met with a WSOD, and this message:
"The website encountered an unexpected error. Please try again later."

I then see these entries in the error log.  

What am I over looking and how might I resolve it, please?

This is happening for the uid#1 user on login, and regardless of what url is visited.  
It does not impact an anonyous user in a private session.  

-----  


[Mon Oct 26 12:25:33.656979 2020] [proxy_fcgi:error] [pid 35690:tid 139862858528512] [client 172.17.0.4:48496] 
AH01071: Got error 'PHP message: Error: Call to a member function toUrl() on null in 
/opt/local/jf4ga/drupal/web/core/modules/shortcut/shortcut.module on line 401 
#0 [internal function]: shortcut_toolbar()\n
#1 /opt/local/jf4ga/drupal/web/core/lib/Drupal/Core/Extension/ModuleHandler.php(403): call_user_func_array('shortcut_toolba...', Array)\n
#2 /opt/local/jf4ga/drupal/web/core/modules/toolbar/src/Element/Toolbar.php(81): Drupal\\Core\\Extension\\ModuleHandler->invokeAll('toolbar')\n
#3 [internal function]: Drupal\\toolbar\\Element\\Toolbar::preRenderToolbar(Array)\n
#4 /opt/local/jf4ga/drupal/web/core/lib/Drupal/Core/Security/DoTrustedCallbackTrait.php(100): call_user_func_array(Array, Array)\n
#5 /opt/local/jf4ga/drupal/web/core/lib/Drupal/Core/Render/Renderer.php(781): Drupal\\Core\\Render\\Renderer->doTrustedCallback(Array, Array, 'Render #pre_ren...', 'silenced_deprec...', 'Drupal\\\\Core\\\\Ren...')\n
#6 /opt/local/jf4ga/drupal/web/core/lib/Drupal/Core/Render/Renderer.php(372): Drupal\\Core\\Render\\Renderer->doCallback('#pre_render', Ar...'

0200-shortcut--shortcut.module

---  shortcut/shortcut.module on line 401 

/**
 * Returns the current displayed shortcut set for the provided user account.
 *
 * @param $account
 *   (optional) The user account whose shortcuts will be returned. Defaults to
 *   the currently logged-in user.
 *
 * @return
 *   An object representing the shortcut set that should be displayed to the
 *   current user. If the user does not have an explicit shortcut set defined,
 *   the default set is returned.
 */
function shortcut_current_displayed_set($account = NULL) {
  $shortcut_sets = &drupal_static(__FUNCTION__, []);
  $user = \Drupal::currentUser();
  if (!isset($account)) {
    $account = $user;
  }
  // Try to return a shortcut set from the static cache.
  if (isset($shortcut_sets[$account->id()])) {
    return $shortcut_sets[$account->id()];
  }
  // If none was found, try to find a shortcut set that is explicitly assigned
  // to this user.
  $shortcut_set_name = \Drupal::entityTypeManager()
    ->getStorage('shortcut_set')
    ->getAssignedToUser($account);
  if ($shortcut_set_name) {
    $shortcut_set = ShortcutSet::load($shortcut_set_name);
  }
  // Otherwise, use the default set.
  else {
    $shortcut_set = shortcut_default_set($account);
  }

  $shortcut_sets[$account->id()] = $shortcut_set;
  return $shortcut_set;
}

<snip>

/**
 * Implements hook_toolbar().
 */
function shortcut_toolbar() {
  $user = \Drupal::currentUser();

  $items = [];
  $items['shortcuts'] = [
    '#cache' => [
      'contexts' => [
        'user.permissions',
      ],
    ],
  ];

  if ($user->hasPermission('access shortcuts')) {
    $shortcut_set = shortcut_current_displayed_set();

    $items['shortcuts'] += [
      '#type' => 'toolbar_item',
      'tab' => [
        '#type' => 'link',
        '#title' => t('Shortcuts'),
        '#url' => $shortcut_set->toUrl('collection'),  // <<<--- line 401 
        '#attributes' => [
          'title' => t('Shortcuts'),
          'class' => ['toolbar-icon', 'toolbar-icon-shortcut'],
        ],
      ],
      'tray' => [
        '#heading' => t('User-defined shortcuts'),
        'children' => [
          '#lazy_builder' => ['shortcut.lazy_builders:lazyLinks', []],
          '#create_placeholder' => TRUE,
          '#cache' => [
            'keys' => ['shortcut_set_toolbar_links'],
            'contexts' => ['user'],
          ],
        ],
      ],
      '#weight' => -10,
      '#attached' => [
        'library' => [
          'shortcut/drupal.shortcut',
        ],
      ],
    ];
  }

  return $items;
}