I can confirm this error.

Taking note of the error , and comparing your code with the scrappy generated code, and I see it wants a session file, so I add

my $sess = 'foo.scrappy.session';
-f $sess
? $scraper->session->load($sess)
: $scraper->session->write($sess);
[download]

and the error goes away. Its some kind of bug (either session is required, or its optional, or somethiing else).