From 9fbaf2d2ea49adb97cc45be83a966fb3c7f292f2 Mon Sep 17 00:00:00 2001
From: "Eric N. Vander Weele" <ericvw@gmail.com>
Date: Sun, 28 Jul 2019 10:39:27 -0400
Subject: [PATCH] utils: Assert desired contract for
 `parse_comma_separated_list()`

This is a separate commit so it can be dropped during a rebase or
reverted independently.
---
 src/flake8/utils.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index 02f0607..cf88648 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -39,6 +39,10 @@ def parse_comma_separated_list(value, regexp=COMMA_SEPARATED_LIST_RE):
     :rtype:
         list
     """
+    assert isinstance(  # nosec (for bandit)
+        value, (string_types, type(None))
+    ), value
+
     if not value:
         return []