diff --git a/simpleeval.py b/simpleeval.py
index 756f04b..46c3f76 100644
--- a/simpleeval.py
+++ b/simpleeval.py
@@ -225,7 +225,7 @@
         "real",
         "to_bytes",
     },
-    None: {},
+    None: set(),
     dict: {
         "clear",
         "copy",