Warnings when Facets view mode processor is enabled

Problem/Motivation

When Facets view mode processor (Transform entity ID to view mode) is enabled, these warnings occur:

Warning: preg_split() expects parameter 2 to be string, array given in Drupal\Component\Transliteration\PhpTransliteration->removeDiacritics() (line 94 of core/lib/Drupal/Component/Transliteration/PhpTransliteration.php).

Warning: Invalid argument supplied for foreach() in Drupal\Component\Transliteration\PhpTransliteration->removeDiacritics() (line 94 of core/lib/Drupal/Component/Transliteration/PhpTransliteration.php).

Steps to reproduce

1. Create / edit a facet
2. Enable "Transform entity ID to view mode" option