From zefram@fysh.org

$ ./perl6 -e 'my Int $a is default(Nil); say $a'
===SORRY!=== Error while compiling -e
Default value '(Any)' will never bind to a parameter of type Int
at -e​:1
------> my Int $a is default(Nil)^; say $a
  expecting any of​:
  constraint

The error message is correct that this is a bad default value for
the variable's type, but it is incorrect in identifying the value.
The failure mode looks very much like [perl #​126091], which occurred in
a situation where Nil was a type constraint.

-zefram

From @usev6

The correct default value Nil is now mentioned in the error message​:

$ perl6-m -e 'my Int $a is default(Nil)'
===SORRY!=== Error while compiling -e
Default value 'Nil' will never bind to a parameter of type Int
at -e​:1
------> my Int $a is default(Nil)⏏<EOL>
  expecting any of​:
  constraint

I added a test to S32-exceptions/misc.t with commit Raku/roast@01a65f421d

I'm closing this ticket as 'resolved'.

@usev6 - Status changed from 'new' to 'resolved'