I dunno, but doesn't the cgi param function already return an undef when you pass it a bogus param name? In this case wouldn't it be okay to do the following without extra hash creation:

#!/usr/bin/perl -w
use strict;
use CGI;
#using params in a file 'cause I don't have a webserver handy
open(INPUTFILE,"c:\\temp\\inputs.dat");
 my $cgi = new CGI(\*INPUTFILE);
close(INPUTFILE);

my @keywords = qw~man dog horse barker~;

foreach(@keywords) {
    
    if (!defined($cgi->param($_)) || $cgi->param($_) eq ' ' || $cgi->p
+aram($_) eq '' ) {
    print "Nothing there for $_!\n";
    }
}
#contents of the .dat file are
#man=horse 
#dog=man 
#horse=
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