[perl #132082] [BUG] "is default(Mu)" parse failure when used on attribute

[Brian S. Julin]

# New Ticket Created by  "Brian S. Julin" 
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"is default(Mu)" works fine on a variable, but runs into syntax issues on 
attributes...
weirdly... only for Mu.

$ perl6 -e 'my $a is default(Mu);'
$ perl6 -e 'class A { has $.a is default(Mu); }'
===SORRY!=== Error while compiling -e
Can't use unknown trait 'is default' in an attribute declaration.
at -e:1
    expecting any of:
        rw
        readonly
        box_target
        leading_docs
        trailing_docs
$ perl6 -e 'class A { has $.a is default(Nil); }'
$

I will be adding fudged tests to S02-names/is_default.t for this.