Fix 'call to undefined function l()'.
Fix theme functions does not work.
Fix 'call to undefined function l()'.
Fix requesting a non-existent service 'book.manager'.
Fix 'call to undefined function url()'.
Fix 'Cannot use object of type FormState as array'.
Fix 'Call to undefined method Drupal\Core\Menu\MenuLinkDefault::isHidden()'.
Fix 'Call to undefined method Drupal\Core\Utility\LinkGenerator::generateFromUrl()'.
Fix 'Cache tags must be strings, array given.'.