mariadb-dump creates empty backup without error message/code

Example (binary logs enabled):

1. mariadb-dump --user=root --all-databases --flush-logs --master-data=1 --events --triggers --routines > /tmp/full_dump.sql
2. echo $?
   0
3. ls -lah /tmp/full_dump.sql
   rw-rr- 1 root root 1.3K May 30 14:56 /tmp/full_dump.sql

Backup is nearly empty...

Reason:

SQL> FLUSH LOGS;
ERROR 1004 (HY000): Can't create file '/var/log/mysqld_error.log' (errno: 13 "Permission denied")

This is really ugly. I would expect a return code Unable to render embedded object: File (= 0 AND an error message) not found.