diff --git a/src/AliasCleaner.php b/src/AliasCleaner.php
--- a/src/AliasCleaner.php
+++ b/src/AliasCleaner.php
@@ -133,7 +133,7 @@
     $config = $this->configFactory->get('pathauto.settings');

     if (!isset($separator)) {
-      $separator = $config->get('separator');
+      $separator = (string)$config->get('separator');
     }

     $output = $string;
@@ -170,7 +170,7 @@
       // Generate and cache variables used in this method.
       $config = $this->configFactory->get('pathauto.settings');
       $this->cleanStringCache = [
-        'separator' => $config->get('separator'),
+        'separator' => (string)$config->get('separator'),
         'strings' => [],
         'transliterate' => $config->get('transliterate'),
         'punctuation' => [],
@@ -200,7 +200,7 @@
       }

       // Generate and cache the ignored words regular expression.
-      $ignore_words = $config->get('ignore_words');
+      $ignore_words = (string)$config->get('ignore_words');
       $ignore_words_regex = preg_replace(['/^[,\s]+|[,\s]+$/', '/[,\s]+/'], ['', '\b|\b'], $ignore_words);
       if ($ignore_words_regex) {
         $this->cleanStringCache['ignore_words_regex'] = '\b' . $ignore_words_regex . '\b';
diff --git a/src/Form/PathautoSettingsForm.php b/src/Form/PathautoSettingsForm.php
--- a/src/Form/PathautoSettingsForm.php
+++ b/src/Form/PathautoSettingsForm.php
@@ -150,7 +150,7 @@
         $form['enabled_entity_types'][$entity_type_id] = [
           '#type' => 'checkbox',
           '#title' => $entity_type->getLabel(),
-          '#default_value' => isset($field_definitions['path']) || in_array($entity_type_id, $config->get('enabled_entity_types')),
+          '#default_value' => isset($field_definitions['path']) || in_array($entity_type_id, (array)$config->get('enabled_entity_types')),
           '#disabled' => isset($field_definitions['path']) && ($field_definitions['path']->getProvider() != 'pathauto' || $patterns_count),
         ];
       }
@@ -252,7 +252,7 @@
     $form['safe_tokens'] = [
       '#type' => 'textarea',
       '#title' => $this->t('Safe tokens'),
-      '#default_value' => implode(', ', $config->get('safe_tokens')),
+      '#default_value' => implode(', ', (array)$config->get('safe_tokens')),
       '#description' => $this->t('List of tokens that are safe to use in alias patterns and do not need to be cleaned. For example urls, aliases, machine names. Separated with a comma.'),
     ];