Bad "default-character-set" option in [client] option group 50-client.cnf on Debian/Ubuntu

$ cat /etc/mysql/mariadb.conf.d/50-client.cnf 

#

# This group is read by the client library

# Use it for options that affect all clients, but not the server

#

[client]

# Default is Latin1, if you need UTF-8 set this (also in server section)

default-character-set = utf8mb4

# Example of client certificate usage

# ssl-cert=/etc/mysql/client-cert.pem

# ssl-key=/etc/mysql/client-key.pem

#

# Allow only TLS encrypted connections

# ssl-verify-server-cert=on

# This group is *never* read by mysql client library, though this

# /etc/mysql/mariadb.cnf.d/client.cnf file is not read by Oracle MySQL

# client anyway.

# If you use the same .cnf file for MySQL and MariaDB,

# use it for MariaDB-only client options

[client-mariadb]

$ mysqlbinlog --help 

mysqlbinlog: unknown variable 'default-character-set=utf8mb4'

$ mysqlslap --help 

mysqlslap: unknown variable 'default-character-set=utf8mb4'