The condition for autovivification is not meet in this case. See below demo:

use Data::Dumper;
use strict;
use warnings;

my $a = ["abc","cba"];
if (defined($a->[2]) && $a->[2] ne '') {
}
print Dumper($a);
if (defined($a->[2]->[3]) && $a->[2]->[3] ne '') {#this is autovivific
+ation
}
print Dumper($a);
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Here is the result from above code:

$VAR1 = [
          'abc',
          'cba'
        ];
$VAR1 = [
          'abc',
          'cba',
          []   #this is autovivification
        ];
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Autovivification doesn't happen in this case, e.g.

my $foo = [qw(a b c)];
if (defined $foo->[4]) {
    print "this will not print\n";
}
print join('|', @$foo), "\n";
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... prints "a|b|c" instead of "a|b|c||" as you would expect if autovivification had occurred.