double free error in gawk

[NIDE, Naoyuki]

Hello,
gawk causes a double free error with the -M option and a certain program.

$ LC_ALL=C gawk -M 'BEGIN{$0 = "a0 b"; gsub(/0/, "", $1); $2 == "b"; $0 = ""}'
free(): double free detected in tcache 2
Aborted (core dumped)
$ LC_ALL=C gawk --version
GNU Awk 5.1.0, API: 3.0 (GNU MPFR 3.1.6-p2, GNU MP 6.1.2)
Copyright (C) 1989, 1991-2020 Free Software Foundation.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.

-- 
NIDE, Naoyuki
nide@ics.nara-wu.ac.jp