Passing C<undef> to a subroutine now causes @_ to contain the same read-only undefined scalar that C<undef> returns. Furthermore, C<exists $_[0]> will now return true if C<undef> was the first argument.
[perl #7508, #109726].
+=item *
+
+Passing a nonexistent array element to a subroutine does not usually
+autovivify it unless the subroutine modifies its argument. This did not
+work correctly with negative indices and with nonexistent elements within
+the array. The element would be vivified immediately. The delayed
+vivification has been extended to work with those. [perl #118691]
+
=back
=head1 Known Problems