[perl #119643] [BUG] Null PMC access when composing a stubbed role into a class in Rakudo

[Carl Mäsak]

# New Ticket Created by  "Carl Mäsak" 
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<lizmat> r: my role Foo { ... }; class A does Foo {}  # seems we can't
compose with a stubbed role
<camelia> rakudo 044bd5: OUTPUT«===SORRY!===␤None of the parametric
role variants for 'Foo' matched the arguments supplied.␤Null PMC
access in get_pmc_keyed()␤»
* masak submits rakudobug

Two things:

(a) the Null PMC access
(b) the error message not being very descriptive as to what's wrong