Improve log message when failing to create backup ref

Change-Id: I077018799b92a4da83317cf053121dbeed0d6de6
diff --git a/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java b/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java
index 30e40ca..704ae5c 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java
@@ -171,7 +171,7 @@
               | IOException
               | PermissionBackendException
               | NoSuchProjectException e) {
-            log.error(e.getMessage(), e);
+            log.error("Failed to create backup ref {}", backupRef, e);
           }
         }
       }