Perl will only autovivify the anon. array if the value of the array element is undefined. if it has any value that would test as defined, including '' & 0, it will issue a warning.

Actually, perl will die, not issue a warning:

Can't use string (""%s"") as %s ref while ""strict refs"" in use

(F) Only hard references are allowed by "strict refs". Symbolic references are disallowed. See the perlref manpage. - perldiag

That (F) means A fatal error (trappable), i.e. die.

Programmer beware.