That is impossible.
1. The html is broken (no form tags),
which is why there is no default form,
to be set as default, or for you to select
(via $mech->form_name or $mech->form_number
and why $mech->click
This is a bug in WWW::Mechanize, it should throw a useful error messages, example
$ua->get('http://search.cpan.org');#got a form
$ua->get('http://cpan.org');#no forms here
warn $ua->submit; #dies here
HTML::Form=HASH(0x1d76ca0) at - line 6.
HTTP::Response=HASH(0x1d77114) at - line 7.
Warning: something's wrong at - line 9.
Can't call method "make_request" on an undefined value at D:/Perl/site
+/lib/WWW/Mechanize.pm line 1641.