Issue #3092530 by Grayle: Allow empty 'replace' patterns for MachineName render element

core/lib/Drupal/Core/Render/Element/MachineName.php

@@ -245,7 +245,7 @@ public static function processMachineName(&$element, FormStateInterface $form_st
    */
   public static function validateMachineName(&$element, FormStateInterface $form_state, &$complete_form) {
     // Verify that the machine name not only consists of replacement tokens.
-    if (preg_match('@^' . $element['#machine_name']['replace'] . '+$@', $element['#value'])) {
+    if (!empty($element['#machine_name']['replace']) && preg_match('@^' . $element['#machine_name']['replace'] . '+$@', $element['#value'])) {
       $form_state->setError($element, t('The machine-readable name must contain unique characters.'));
     }