And in addition to the others, there is yet another little mistake in your script:

my %form_values="";
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If you want to initialize an empty error, it's better to use

my %form_values;  # just that, now it's empty
# or
my %form_values = (); # so that everybody knows you really wanted that
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Your instead is interpreted by perl as

my %form_values = ("" => undef);
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what is perhaps not what you meant.
BTW: Perl would have also told you that if you have switched warnings on :-)

Greetings,
Janek