automysqlbackup file empty

I recently set up automysqlbackup on a Ubuntu server.

The script runs fine and doesn't report any errors-- it creates the tar.gz file as expected. However, when I extract the actual sql file from the archive, it is a zero-length file.

Is there anything obvious that I'm missing in the configs?

Here's the only parts of the config file I modified:

# Username to access the MySQL server e.g. dbuser
USERNAME=myusername

# Username to access the MySQL server e.g. password
PASSWORD=mypass

# Host name (or IP address) of MySQL server e.g localhost
DBHOST=mysql.remotehost.com

# List of DBNAMES for Daily/Weekly Backup e.g. "DB1 DB2 DB3"
# Note that it's absolutely normal that the db named "mysql" is not in this
# list, as it's added later by the script. See the MDBNAMES directives below
# in this file (advanced options).
# This is ONLY a convenient default, if you don't like it, don't complain
# and write your own.
# The following is a quick hack that will find the names of the databases by
# reading the mysql folder content. Feel free to replace by something else.
# This one does a list of dbs using a MySQL statement.
DBNAMES='mydbname'

# Backup directory location e.g /backups
# Folders inside this one will be created (daily, weekly, etc.), and the
# subfolders will be database names. Note that backups will be owned by
# root, with Unix rights 0600.
BACKUPDIR='/home/myuser/automysqlbackup'