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sub BUILDARGS {
    my $class = shift;
...
    $args{code} = uc $args{code} if exists $args{code};
    return \%args;
}

package UpperCaseDemo;
use Moose;
...
my $cc = UpperCaseDemo->new_with_options();

print "code is ", $cc->code // 'not set', "\n";