SF #515023.  Make _DummyThread.join() signature match base class (Thread)
diff --git a/Lib/threading.py b/Lib/threading.py
index 6543cc3..9763c62 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -572,7 +572,7 @@
     def _set_daemon(self):
         return 1
 
-    def join(self):
+    def join(self, timeout=None):
         assert 0, "cannot join a dummy thread"