allow undef as an arg to '&' prototype

RT #123475

Commit e41e9865be5555 (to fix [perl #123062]) restricted the types of
args allowed for a function with a '&' prototype - previously it allowed
array refs and the like. It also removed undef, so this was now a
compile-time error:

    sub foo (&) {...}
    foo(undef)

However, some CPAN code used the idiom register_callback(undef) to
explicitly disable a registered callback.

So re-allow an explicit undef.

0 files changed, 0 insertions, 0 deletions