diff --git a/includes/Admin/Cross_Origin_Isolation.php b/includes/Admin/Cross_Origin_Isolation.php
index 52cd3f5d9f52..69a005405f6d 100644
--- a/includes/Admin/Cross_Origin_Isolation.php
+++ b/includes/Admin/Cross_Origin_Isolation.php
@@ -291,7 +291,7 @@ protected function replace_in_dom( string $html ): string { // phpcs:ignore Slev
 				}
 
 				$attribute = $match_value[1];
-				$value     = $match_value[4] ?? $match_value[3];
+				$value     = $match_value[4] ?? $match_value[3] ?? '';
 				$cache_key = 'video' === $tag || 'audio' === $tag ? $tag : $attribute;
 
 				// If already processed tag/attribute and value before, skip.
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index 3f0c8f4d2db3..4c0f4ea70ac4 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -20,9 +20,6 @@ parameters:
     -
       message: '/^Parameter #2 \$args of method WP_Customize_Manager::add_setting\(\)/'
       path: includes/Admin/Customizer.php
-    -
-      message: '/^Casting class ReflectionType to string is deprecated\.$/'
-      path: includes/Infrastructure/Injector/SimpleInjector.php
     -
       message: '/\(int\) does not accept int\|WP_Error\.$/'
       path: tests/phpunit/integration/tests