diff --git a/java/com/google/gitiles/dev/DevServer.java b/java/com/google/gitiles/dev/DevServer.java
index 028edd6..675511b 100644
--- a/java/com/google/gitiles/dev/DevServer.java
+++ b/java/com/google/gitiles/dev/DevServer.java
@@ -212,7 +212,7 @@
 
         @Override
         public Object getUserKey() {
-          return null;
+          return "";
         }
 
         @Override