[perl #96424] NULL PMC on unmatched or non existent named capture

[Ron Schmidt via RT]

Seems at least partially fixed in nom but still may be related concerns 
like

nom: my $m = '34' ~~ /<digit>+|<alpha>+/; say $m<alpha>.perl; say 
Nil.perl; my $x = $m<alpha> // 4; say 'x is ', $x
nom: OUTPUT«()␤Nil␤x is ␤»

See http://irclog.perlgeek.de/perl6/2011-08-07#i_4239512