Comparing possibly empty string sequences

Hey list,

a question somewhat related to my previous one.
Say I have $classes, a sequence of classnames (strings), possibly empty.

Now I want to select elements which @class attribute contains any of
the classnames from $class:
h:*[@class/tokenize(., '\s+') = $break-classes)]

In other words, select elements where tokenized @class intersects with $class.

It works fine unless $classes is an empty sequence, in which case I
get an error:
"XTTE0570: An empty sequence is not allowed as the value of variable $classes"

Any way to handle empty sequences in this situation as well? Could
intersect() be a better option here?

Thanks,

Martynas
odt2epub.com