Never bind a Mu into Hash's $!storage

Just leave it unset, and it'll vivify on demand if needed.

src/Perl6/Metamodel/BOOTSTRAP.nqp

@@ -744,7 +744,7 @@ my class Binder {
                 # that. Otherwise, putting Mu in there is fine; Hash is smart
                 # enough to know what to do.
                 my $hash := nqp::create(Hash);
-                nqp::bindattr($hash, Map, '$!storage', $named_args || Mu);
+                nqp::bindattr($hash, Map, '$!storage', $named_args) if $named_args;
                 $bind_fail := bind_one_param($lexpad, $sig, $param, $no_nom_type_check, $error,
                     0, $hash, 0, 0.0, '');
                 return $bind_fail if $bind_fail;