diff -r c089a0947f3e -r f7459da77f23 mercurial/debugcommands.py
--- a/mercurial/debugcommands.py	Fri Feb 14 15:03:26 2020 +0100
+++ b/mercurial/debugcommands.py	Tue Feb 11 11:18:52 2020 +0100
@@ -2122,7 +2122,7 @@
         nm_data = nodemap.persisted_data(cl)
         if nm_data is not None:
             docket, data = nm_data
-            ui.write(data)
+            ui.write(data[:])
     elif opts['check']:
         unfi = repo.unfiltered()
         cl = unfi.changelog