result is undefined

occ.py

diff --git a/occ.py b/occ.py
index 10e68fd..ad78c5c 100644
--- a/occ.py
+++ b/occ.py
@@ -89,7 +89,7 @@
         raise CommandException("Subprocess error - unable to change to user %s for running command (permission denied?)" % username, 7)
     if process.returncode != 0:
         print("on-commit command failed with exit code %d!" % process.returncode)
-        raise CommandException(result[0].decode('utf-8'), process.returncode)
+        raise CommandException(stderr_data.decode('utf-8'), process.returncode)
 
 
 def change_user(user_uid, user_gid):