[perl #100472] [BUG] Undefined interpolated values in regexes wrongly match in Rakudo

[Carl Mäsak]

# New Ticket Created by  "Carl Mäsak" 
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<moritz> nom: say 'aa' ~~ /(.)$1/
<p6eval> nom ebd4d8: OUTPUT«=> <a>␤ 0 => <a>␤␤»
<moritz> this... shouldn't match
<moritz> nom: my $a; say so  'aaa' ~~ /$a/
<p6eval> nom ebd4d8: OUTPUT«Use of uninitialized value in string
context␤Use of uninitialized value in string context␤Bool::True␤»
<moritz> RONG
* masak submits rakudobug

I guess the correct behavior of an undefined interpolated value is
simply to always fail that part of the match.