diff --git a/src/applications/diffusion/data/DiffusionCommitRef.php b/src/applications/diffusion/data/DiffusionCommitRef.php
--- a/src/applications/diffusion/data/DiffusionCommitRef.php
+++ b/src/applications/diffusion/data/DiffusionCommitRef.php
@@ -130,7 +130,9 @@
       $this->getMessage());
   }
 
-  private function formatUser($name, $email) {
+  private function formatUser($name = '', $email = '') {
+    $name = coalesce($name, '');
+    $email = coalesce($email, '');
     if (strlen($name) && strlen($email)) {
       return "{$name} <{$email}>";
     } else if (strlen($email)) {