git commit -m 'Issue #3253777 by balis_m, AdamPS: Notice: Undefined index: bcc...

git commit -m 'Issue #3253777 by balis_m, AdamPS: Notice: Undefined index: bcc in Drupal\symfony_mailer\Email->getParam()' --author="balis_m <balis_m@2664243.no-reply.drupal.org>"

src/BaseEmailInterface.php

@@ -89,7 +89,7 @@ interface BaseEmailInterface {
    *   Parameter key to get.
    *
    * @return mixed
-   *   Parameter value.
+   *   Parameter value, or NULL if the parameter is not set.
    */
   public function getParam(string $key);
 

src/Email.php

@@ -298,7 +298,7 @@ class Email implements UnrenderedEmailInterface, RenderedEmailInterface {
    * {@inheritdoc}
    */
   public function getParam(string $key) {
-    return $this->params[$key];
+    return $this->params[$key] ?? NULL;
   }
 
   /**