Add obvious needed else clause to format_exception().
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 7fc209e..70d3230 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -87,6 +87,8 @@
 	if tb:
 		list = ['Traceback (innermost last):\n']
 		list = list + format_tb(tb, limit)
+	else:
+		list = []
 	list = list + format_exception_only(etype, value)
 	return list