--- 2843327-34.patch	2018-07-10 20:50:17.020362400 +0100
+++ swiftmailer.css_inliner.2843327-49.patch	2018-07-10 20:50:04.265940100 +0100
@@ -263,7 +263,7 @@ index 3e89311..ba18a41 100644
 +      if ($this->config['message']['css_inliner']) {
 +        $message['body'] = (new CssToInlineStyles())->convert($message['body'], $css);
 +      }
-+      else {
++      elseif ($css)  {
 +        // Insert the CSS into the header with a style element.
 +        $dom = new \DOMDocument();
 +        @$dom->loadHTML($message['body']);