[perl #73940] [BUG] LTA error message when parsing empty () or [] in a regex in Rakudo

[Carl Mäsak]

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<masak> std: "abc" ~~ /()/
<p6eval> std 30251: OUTPUT«===SORRY!===␤Null pattern
not allowed [...] FAILED 00:01 107m␤»
<masak> rakudo: "abc" ~~ /()/
<p6eval> rakudo 872898: OUTPUT«Confused [...]
* masak submits LTA rakudobug
<masak> rakudo: "abc" ~~ /[]/
<p6eval> rakudo 872898: OUTPUT«Confused [...]

This all comes down to how nqp-rx parses regexes. It can do it
slightly more informatively in the case of empty () and [].