[perl #63894] A returned () is a Nil but doesn't smartmatch against one

[Carl Mäsak]

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<masak> rakudo: sub foo { return }; say foo.WHAT; say ?(foo ~~ Nil)
<p6eval> rakudo 5b1ff9: OUTPUT«Nil␤0␤»
* masak submits

Expected behavior: a "Nil" and a 1. Or an explanation about why a
value shouldn't smartmatch successfully against its own type.