diff -r 4db5671d57d9 -r 330c258fe7ca mercurial/ui.py
--- a/mercurial/ui.py	Sat Oct 17 21:57:21 2020 +0900
+++ b/mercurial/ui.py	Thu Oct 29 00:17:12 2020 -0700
@@ -1661,7 +1661,9 @@
             if not r:
                 r = default
             if self.configbool(b'ui', b'promptecho'):
-                self._writemsg(self._fmsgout, r, b"\n", type=b'promptecho')
+                self._writemsg(
+                    self._fmsgout, r or b'', b"\n", type=b'promptecho'
+                )
             return r
         except EOFError:
             raise error.ResponseExpected()