Issue #14605: Use None in sys.path_importer_cache to represent no
finder instead of using some (now non-existent) implicit finder.
diff --git a/Modules/main.c b/Modules/main.c
index 6eb05e9..e262552 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -224,7 +224,7 @@
     if (importer == NULL)
         goto error;
 
-    if (importer->ob_type == &PyNullImporter_Type) {
+    if (importer == Py_None) {
         Py_DECREF(argv0);
         Py_DECREF(importer);
         return -1;