From 91deb7a79f9eff58a8ff02566e7da9eb06a99ec6 Mon Sep 17 00:00:00 2001
From: Thomas Schaper <libre-man@users.noreply.github.com>
Date: Sun, 16 Feb 2020 19:40:10 +0100
Subject: [PATCH] Make `FrameType.f_back` optional (#3740)

---
 stdlib/3/types.pyi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stdlib/3/types.pyi b/stdlib/3/types.pyi
index b8f7d925a..f826ce91d 100644
--- a/stdlib/3/types.pyi
+++ b/stdlib/3/types.pyi
@@ -248,7 +248,7 @@ class TracebackType:
     def tb_lineno(self) -> int: ...
 
 class FrameType:
-    f_back: FrameType
+    f_back: Optional[FrameType]
     f_builtins: Dict[str, Any]
     f_code: CodeType
     f_globals: Dict[str, Any]