diff --git a/src/infrastructure/editor/PhabricatorEditorURIEngine.php b/src/infrastructure/editor/PhabricatorEditorURIEngine.php
--- a/src/infrastructure/editor/PhabricatorEditorURIEngine.php
+++ b/src/infrastructure/editor/PhabricatorEditorURIEngine.php
@@ -141,10 +141,12 @@
 
     $variables = array(
       'r' => $this->escapeToken($repository->getCallsign()),
-      'n' => $this->escapeToken($repository->getRepositorySlug()),
       'd' => $this->escapeToken($repository->getID()),
       'p' => $this->escapeToken($repository->getPHID()),
     );
+    if ($repository->getRepositorySlug()) {
+      $variables['n'] = $this->escapeToken($repository->getRepositorySlug());
+    }
 
     return $this->newTokensWithVariables($tokens, $variables);
   }