Consider that the code 

#! /usr/bin/perl
use strict;
use warnings;

print scalar @ARGV, "\n"

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outputs 0. By explicitly accessing the non-existent array element, perl extends the array and populates those new values with undefs, and that is what gets passed to your subroutine. This is a manifestation of autovivification.. As ikegami points out, this isn't autovivification, but it is returning an undef as you attempt to access the undefined array element.

In reply to Re: Question: Is undef a valid argument? by kennethk
in thread Question: Is undef a valid argument? by jujiro_eb

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