"Instance of Cpanel::Email::Privs destroyed without save" error appears on the Webmail landing page

Symptoms

An error like this one appears on the Webmail landing page, as well as in the cPanel error log:

warn [Internal Warning while parsing ./webmail/paper_lantern/index.html
3332563] WARNING: Instance of Cpanel::Email::Privs destroyed without save().
Aborting transaction. at /usr/local/cpanel/Cpanel/Email/Privs.pm line 117.
at /usr/local/cpanel/Cpanel/Email/Privs.pm line 117.
Cpanel::Email::Privs::DESTROY(Cpanel::Email::Privs=HASH(0x317b930)) called
at /usr/local/cpanel/Cpanel/Transaction/File/BaseReader.pm line 60
eval {...} called at /usr/local/cpanel/Cpanel/Transaction/File/BaseReader.pm line 60

Description

This error is caused by a corrupted _privs.json file in the domain's mail directory:

[root@server]# python -m json.tool /home/$user/etc/$domain/_privs.json
No JSON object could be decoded

Workaround

Move aside the corrupted file. Make sure to replace $user with the username and $domain with the domain name:

mv -v /home/$user/etc/$domain/_privs.json /root