different values - including 0 - are considered false in Perl but not the other way round.

DB<9> use Data::Dump "dd"

DB<10> dd { true => !0, false => !1 }       
{ false => "", true => 1 }
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If you want Perl's internal value for false˛ to be mapped to 0 you have to do a $porter ||= 0

˛) NB: magical value! It is more than just an empty string to evaluate correctly in different contexts.