/usr/bin/vbackup-wizard: line 270: -z: command not found

[vazhnov]

I'm trying to use vbackup 1.0.1 in Xubuntu 16.04.
Every time I run vbackup-wizard, it return error:

vbackup stores all backups under a common directory prefix. Please enter a
prefix where all backups will be placed under. Be carefull not to use a path
that is been backed up or you will create a backup paradox.

The best place to store backups is an external disk or a remote directory that
is localy mounted

Where to place backups? /mnt
/usr/bin/vbackup-wizard: line 270: -z: command not found

I think that line 270 should be:

	if ! [ -z "$STRATEGY" ] ; then