param('noSuchKey') seems to return undef if there is no such field, so you can use defined:
my $param = param('whatever');
if (!defined($param)) { # do something
}

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In reply to Re: Any Way To Distinguish Undef From Empty Parameters When Using CGI.pm's Param() function? by bikeNomad
in thread Any Way To Distinguish Undef From Empty Parameters When Using CGI.pm's Param() function? by sierrathedog04

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