Perl distinguishes between a capture that wasn't encountered in the match and a capture that matched zero characters.
use Data::Dumper qw( Dumper );
'' =~ /
) # $2
) # $1
local $Data::Dumper::Useqq = 1;
local $Data::Dumper::Terse = 1;
local $Data::Dumper::Indent = 0;
print('$1 = ', Dumper($1), "\n");
print('$2 = ', Dumper($2), "\n");
$1 = ""
$2 = undef
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