lesson_check: fix create_checker function

diff --git a/bin/lesson_check.py b/bin/lesson_check.py
index 441c1a71fb568837ecb3d988388af804e5f73469..d179db519bd399bc2a0ddd42d193edb31e05b54d 100755 (executable)
--- a/bin/lesson_check.py
+++ b/bin/lesson_check.py
@@ -271,7 +271,7 @@ def create_checker(args, filename, info):
     for (pat, cls) in CHECKERS:
         if pat.search(filename):
             return cls(args, filename, **info)
-
+    return NotImplemented
 
 class CheckBase(object):
     """Base class for checking Markdown files."""