[Boston.pm] catenation of undef with string, 2 cases

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

my $a;
$a .= '70';
my $b;
$b = 42 . $b;
print "$a, $b\n";


With the script above I get an uninitialized value warning from perl
5.24 for the second concatenation but not the first. Is there a story
behind this? Something to do with the first case being something you'd
likely want to do without whinging from the interpreter?

- Mike