[lizmat]

FWIW, that was one of the things that Larry fixed in Perl 6 (now the Raku Programming Language https://raku.org #rakulang).

You can bind to a non-existing hash element (even multiple levels deep) and it won't exist until you actually assign to it:

    my %h;
    my $c := %h<a><b><c>;
    say %h<a>:exists;  # False
    $c = 42;
    say %h<a>:exists;  # True