diff -r e8c11a2c96c0 -r bc2519513ae0 mercurial/changegroup.py
--- a/mercurial/changegroup.py	Thu Feb 18 18:18:35 2021 +0100
+++ b/mercurial/changegroup.py	Fri Feb 19 10:53:27 2021 +0100
@@ -945,6 +945,9 @@
         if bundlecaps is None:
             bundlecaps = set()
         self._bundlecaps = bundlecaps
+        if remote_sidedata is None:
+            remote_sidedata = set()
+        self._remote_sidedata = remote_sidedata
         self._isshallow = shallow
         self._fullclnodes = fullnodes