diff --git a/src/PhpWord/TemplateProcessor.php b/src/PhpWord/TemplateProcessor.php
index 664d4688..14c95b18 100644
--- a/src/PhpWord/TemplateProcessor.php
+++ b/src/PhpWord/TemplateProcessor.php
@@ -257,7 +257,7 @@ class TemplateProcessor
      */
     protected static function ensureUtf8Encoded($subject)
     {
-        if (!Text::isUTF8($subject)) {
+        if (!Text::isUTF8($subject) && !is_null($subject)) {
             $subject = utf8_encode($subject);
         }