You seem to have CGI.pm and that old decrepit cgi-lib.pl confused.

CGI.pm is just fine with multiple checkboxes:

@selections = param("state");
[download]

In a scalar context, param returns the first selection it sees. In a list context, it returns the entire list of selections. At no time does anything come back with a NUL separator.

-- Randal L. Schwartz, Perl hacker