That will also convert the string 0 into undef. Fix: 
$sth->execute(
    map { defined($_) && length($_) ? $_ : undef }
        @seen_values );

[download]
or 
$sth->execute(
    map { no warnings 'uninitialized'; length($_) ? $_ : undef }
        @seen_values );

[download]

In reply to Re^2: Want DBI to load empty strings as NULL by ikegami
in thread Want DBI to load empty strings as NULL by Narveson

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