Issue #3432768: Type cast issues when running with PHP 8.2

src/Plugin/Mail/SymfonyMailer.php

@@ -268,7 +268,7 @@ class SymfonyMailer implements MailInterface, ContainerFactoryPluginInterface {
       $this->normalizeHeaders($message);
       if (!empty($message['headers']) && is_array($message['headers'])) {
         foreach ($message['headers'] as $header_key => $header_value) {
-          if (empty($header_key) || in_array($header_key, $headers_to_skip, FALSE)) {
+          if (empty($header_value) || empty($header_key) || in_array($header_key, $headers_to_skip, FALSE)) {
             continue;
           }