diff --git a/src/applications/differential/xaction/DifferentialRevisionActionTransaction.php b/src/applications/differential/xaction/DifferentialRevisionActionTransaction.php
--- a/src/applications/differential/xaction/DifferentialRevisionActionTransaction.php
+++ b/src/applications/differential/xaction/DifferentialRevisionActionTransaction.php
@@ -80,7 +80,7 @@
     DifferentialRevision $revision) {
     return array(
       array(),
-      null,
+      array(),
     );
   }