diff --git a/docs/code/LangFuzzer.py b/docs/code/LangFuzzer.py
index b735a25f4..bbede4288 100755
--- a/docs/code/LangFuzzer.py
+++ b/docs/code/LangFuzzer.py
@@ -427,7 +427,7 @@ def generate_new_tree(self, node, choice):
             if self.check_diversity(pool):
                 return random.choice(self.fragments[name])
             else:
-                return None
+                return (name, None)
         else:
             return (name,
                     [self.generate_new_tree(c, choice) for c in children])