EXCLUDES="" not working

[Niklaas Baudet von Gersdorff]

When using

EXCLUDES=""

I get the following error messages

cannot open 'tank/usr/ports': dataset does not exists
cannot open 'tank/usr/src': dataset does not exist   

The solution to this problem is using

EXCLUDES=" "

Be aware of the white space!

As far as I understand it, the reason for this is

1. The above mentioned datasets do not exist indeed.
2. zfssnap.sh loads the default EXCLUDES when handing over an empty variable.

I guess this should be changed in the documentation or the code updated.

For reference: I already contacted the FreeBSD community here http://docs.freebsd.org/cgi/mid.cgi?20141208191902.GG31701.