+$x # do_nothing($x->[$N[0]]); () # '', undef, [ ]
+$x # do_nothing($x->[$N[0]]); () # '', undef, [ ] #
+$x # do_nothing($x->[$N[0]]); () # '', undef, [ ] # +fetch
+$x # do_nothing($x->[$N[0]]); () # '', undef, [ ] # +exists
+$x # do_nothing($x->[$N[0]]); () # '', undef, [ ] # +delete
+$x # do_nothing($x->[$N[0]]); () # qr/^Can't vivify reference/, undef, undef # +store
+
+$x # set_arg($x->[$N[0]]); () # '', undef, [ 1 ]
+$x # set_arg($x->[$N[0]]); () # '', undef, [ 1 ] #
+$x # set_arg($x->[$N[0]]); () # '', undef, [ 1 ] # +fetch
+$x # set_arg($x->[$N[0]]); () # '', undef, [ 1 ] # +exists
+$x # set_arg($x->[$N[0]]); () # '', undef, [ 1 ] # +delete
+$x # set_arg($x->[$N[0]]); () # qr/^Can't vivify reference/, undef, undef # +store
+