Issue #3027929 - Allow empty messages

src/Plugin/Mail/DrupalPHPMailer.php

@@ -22,6 +22,12 @@ class DrupalPHPMailer extends \PHPMailer implements MailInterface {
 
   use StringTranslationTrait;
 
+  /**
+   * Whether to allow sending messages with an empty body.
+   * @var boolean
+   */
+  public $AllowEmpty = TRUE;
+
   /**
    * Stores the Return-Path, which may be different from Sender.
    */