Issue #14308: Fix an exception when a "dummy" thread is in the threading module's active list after a fork().
diff --git a/Lib/threading.py b/Lib/threading.py
index 69b7763..58ffa7e 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -1007,6 +1007,9 @@
     def _set_daemon(self):
         return True
 
+    def _stop(self):
+        pass
+
     def join(self, timeout=None):
         assert False, "cannot join a dummy thread"