diff --git a/src/applications/differential/editor/DifferentialTransactionEditor.php b/src/applications/differential/editor/DifferentialTransactionEditor.php
--- a/src/applications/differential/editor/DifferentialTransactionEditor.php
+++ b/src/applications/differential/editor/DifferentialTransactionEditor.php
@@ -218,7 +218,8 @@
 
           // No "$", to allow for branches like T123_demo.
           $match = null;
-          if (preg_match('/^T(\d+)/i', $branch, $match)) {
+          if (phutil_nonempty_string($branch) &&
+              (preg_match('/^T(\d+)/i', $branch, $match))) {
             $task_id = $match[1];
             $tasks = id(new ManiphestTaskQuery())
               ->setViewer($this->getActor())