in reply to Perl DBI NULL and undef

undef $_
undefines $_. To test its definedness, use
defined $_
In case of $_, the parameter is optional.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ