diff --git a/src/Form/IndexFieldsForm.php b/src/Form/IndexFieldsForm.php
index 68fac8ad..b82ac27f 100644
--- a/src/Form/IndexFieldsForm.php
+++ b/src/Form/IndexFieldsForm.php
@@ -414,7 +414,7 @@ protected function actions(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
-    $field_values = $form_state->getValues()['fields'];
+    $field_values = $form_state->getValue('fields', []);
     $new_ids = [];
 
     foreach ($field_values as $field_id => $field) {
diff --git a/src/Form/ServerForm.php b/src/Form/ServerForm.php
index e37ad2c2..683c6978 100644
--- a/src/Form/ServerForm.php
+++ b/src/Form/ServerForm.php
@@ -277,7 +277,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       // be discarded.
       $input = &$form_state->getUserInput();
       $input['backend_config'] = [];
-      $new_backend = $this->backendPluginManager->createInstance($form_state->getValues()['backend']);
+      $new_backend = $this->backendPluginManager->createInstance($form_state->getValue('backend'));
       if ($new_backend instanceof PluginFormInterface) {
         $form_state->setRebuild();
       }
diff --git a/src/Plugin/search_api/processor/IgnoreCharacters.php b/src/Plugin/search_api/processor/IgnoreCharacters.php
index 5a21e5df..8cb567fd 100644
--- a/src/Plugin/search_api/processor/IgnoreCharacters.php
+++ b/src/Plugin/search_api/processor/IgnoreCharacters.php
@@ -92,7 +92,7 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
   public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
     parent::validateConfigurationForm($form, $form_state);
 
-    $ignorable = str_replace('/', '\/', $form_state->getValues()['ignorable']);
+    $ignorable = str_replace('/', '\/', $form_state->getValue('ignorable', ''));
     if ($ignorable !== '' && @preg_match('/(' . $ignorable . ')+/u', '') === FALSE) {
       $el = $form['ignorable'];
       $form_state->setError($el, $el['#title'] . ': ' . $this->t('The entered text is no valid regular expression.'));
diff --git a/src/Plugin/search_api/processor/Stopwords.php b/src/Plugin/search_api/processor/Stopwords.php
index 3d9721df..82067057 100644
--- a/src/Plugin/search_api/processor/Stopwords.php
+++ b/src/Plugin/search_api/processor/Stopwords.php
@@ -92,7 +92,11 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
    */
   public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
     // Convert our text input to an array.
-    $form_state->setValue('stopwords', array_filter(array_map('trim', explode("\n", $form_state->getValues()['stopwords'])), 'strlen'));
+    $stopwords = $form_state->getValue('stopwords', '');
+    $stopwords = explode("\n", $stopwords);
+    $stopwords = array_map('trim', $stopwords);
+    $stopwords = array_filter($stopwords, 'strlen');
+    $form_state->setValue('stopwords', $stopwords);
 
     parent::submitConfigurationForm($form, $form_state);
   }
diff --git a/src/Plugin/search_api/processor/Tokenizer.php b/src/Plugin/search_api/processor/Tokenizer.php
index d42ff717..20912cdd 100644
--- a/src/Plugin/search_api/processor/Tokenizer.php
+++ b/src/Plugin/search_api/processor/Tokenizer.php
@@ -115,8 +115,10 @@ public function validateConfigurationForm(array &$form, FormStateInterface $form
     parent::validateConfigurationForm($form, $form_state);
 
     foreach (['spaces', 'ignored'] as $field) {
-      $field_value = str_replace('/', '\/', trim($form_state->getValues()[$field]));
-      if ($field_value !== '' && @preg_match('/[' . $field_value . ']+/u', '') === FALSE) {
+      $field_value = $form_state->getValue($field, '');
+      $field_value = str_replace('/', '\/', trim($field_value));
+      if ($field_value !== ''
+          && @preg_match('/[' . $field_value . ']+/u', '') === FALSE) {
         $form_state->setError($form[$field], $form[$field]['#title'] . ': ' . $this->t('The entered text is no valid PCRE character class.'));
       }
     }