What else would it be?

CRM/Contribute/Form/Task/Invoice.php

@@ -376,7 +376,7 @@ class CRM_Contribute_Form_Task_Invoice extends CRM_Contribute_Form_Task {
         $countryDomain = '';
       }
 
-      $invoiceNotes = Civi::settings()->get('invoice_notes') ?? NULL;
+      $invoiceNotes = Civi::settings()->get('invoice_notes');
 
       // parameters to be assign for template
       $tplParams = [

CRM/Core/Payment/Form.php

@@ -209,7 +209,7 @@ class CRM_Core_Payment_Form {
    */
   public static function buildPaymentForm(&$form, $processor, $billing_profile_id, $isBackOffice, $paymentInstrumentID = NULL) {
     //if the form has address fields assign to the template so the js can decide what billing fields to show
-    $form->assign('profileAddressFields', $form->get('profileAddressFields') ?? NULL);
+    $form->assign('profileAddressFields', $form->get('profileAddressFields'));
     $form->addExpectedSmartyVariable('suppressSubmitButton');
     if (!empty($processor['object']) && $processor['object']->buildForm($form)) {
       return;

ext/oauth-client/tests/phpunit/api/v4/OAuthSessionTokenTest.php

@@ -25,7 +25,7 @@ class api_v4_OAuthSessionTokenTest extends \PHPUnit\Framework\TestCase implement
   public function setUp(): void {
     parent::setUp();
     $this->assertEquals(0, CRM_Core_DAO::singleValueQuery('SELECT count(*) FROM civicrm_oauth_client'));
-    $this->assertNull(CRM_Core_Session::singleton()->get('OAuthSessionTokens') ?? NULL);
+    $this->assertNull(CRM_Core_Session::singleton()->get('OAuthSessionTokens'));
   }
 
   protected function tearDown(): void {