--- a/mercurial/dagop.py Wed Jul 19 13:17:49 2017 -0700
+++ b/mercurial/dagop.py Wed Apr 03 11:21:27 2019 -0700
@@ -764,7 +764,7 @@
the input set.
"""
headrevs = set(revs)
- parents = set([node.nullrev])
+ parents = {node.nullrev}
up = parents.update
for rev in revs: