diff --git a/src/VersionFeed.php b/src/VersionFeed.php
index ad7e1bc..9c7fb2c 100644
--- a/src/VersionFeed.php
+++ b/src/VersionFeed.php
@@ -94,7 +94,7 @@ public function getDiffList($highestVersion = null, $limit = 100)
             if (isset($previous)) {
                 // Produce the diff fields for use in the template.
                 if ($version->Title != $previous->Title) {
-                    $diffTitle = HtmlDiff::compareHTML($version->Title, $previous->Title);
+                    $diffTitle = HtmlDiff::compareHTML($version->Title ?? '', $previous->Title ?? '');
 
                     $version->DiffTitle = DBField::create_field('HTMLText', null);
                     $version->DiffTitle->setValue(
@@ -107,7 +107,7 @@ public function getDiffList($highestVersion = null, $limit = 100)
                 }
 
                 if ($version->Content != $previous->Content) {
-                    $diffContent = HtmlDiff::compareHTML($version->Content, $previous->Content);
+                    $diffContent = HtmlDiff::compareHTML($version->Content ?? '', $previous->Content ?? '');
 
                     $version->DiffContent = DBField::create_field('HTMLText', null);
                     $version->DiffContent->setValue('<div>'.$diffContent.'</div>');