diff -u b/core/lib/Drupal/Core/Database/StatementEmpty.php b/core/lib/Drupal/Core/Database/StatementEmpty.php
--- b/core/lib/Drupal/Core/Database/StatementEmpty.php
+++ b/core/lib/Drupal/Core/Database/StatementEmpty.php
@@ -68,7 +68,7 @@
   /**
    * {@inheritdoc}
    */
-  public function fetchObject(?string $class_name = NULL, ?array $constructor_arguments = NULL) {
+  public function fetchObject(string $class_name = NULL, array $constructor_arguments = NULL) {
     return NULL;
   }
 
diff -u b/core/lib/Drupal/Core/Database/StatementPrefetch.php b/core/lib/Drupal/Core/Database/StatementPrefetch.php
--- b/core/lib/Drupal/Core/Database/StatementPrefetch.php
+++ b/core/lib/Drupal/Core/Database/StatementPrefetch.php
@@ -418,7 +418,7 @@
   /**
    * {@inheritdoc}
    */
-  public function fetchObject(?string $class_name = NULL, ?array $constructor_arguments = NULL) {
+  public function fetchObject(string $class_name = NULL, array $constructor_arguments = NULL) {
     if (isset($this->currentRow)) {
       if (!isset($class_name)) {
         // Directly cast to an object to avoid a function call.
diff -u b/core/lib/Drupal/Core/Database/StatementWrapper.php b/core/lib/Drupal/Core/Database/StatementWrapper.php
--- b/core/lib/Drupal/Core/Database/StatementWrapper.php
+++ b/core/lib/Drupal/Core/Database/StatementWrapper.php
@@ -190,7 +190,7 @@
   /**
    * {@inheritdoc}
    */
-  public function fetchObject(?string $class_name = NULL, ?array $constructor_arguments = NULL) {
+  public function fetchObject(string $class_name = NULL, array $constructor_arguments = NULL) {
     if ($class_name) {
       return $this->clientStatement->fetchObject($class_name, $constructor_arguments);
     }