mariabackup is creating the target-dir when does not exist but not it's parent dir if not exist

it would be expected to create the parent dir(s) from option – target-dir

how to repeat
1. mariabackup -u root -p --backup --target-dir /var/mariadb/backup/ – fails
2. mariabackup -u root -p --backup --target-dir /var/backup – is accepted

mariabackup -u root -p --backup --target-dir /var/mariadb/backup/
180116 15:10:29 Connecting to MySQL server host: localhost, user: root, password: set, port: not set, socket: not set
Using server version 10.2.12-MariaDB
mariabackup based on MariaDB server 10.2.12-MariaDB Linux (x86_64)
mariabackup: uses posix_fadvise().
mariabackup: cd to /var/lib/mysql/
mariabackup: open files limit requested 0, set to 1024
mariabackup: using the following InnoDB configuration:
mariabackup: innodb_data_home_dir = .
mariabackup: innodb_data_file_path = ibdata1:12M:autoextend
mariabackup: innodb_log_group_home_dir = ./
2018-01-16 15:10:29 140226581018752 [Note] InnoDB: Number of pools: 1
mariabackup: Error: cannot mkdir 2: /var/mariadb/backup/