$ perl -Mstrict -Mdiagnostics -wE 'my %foo; say 1 if defined %foo'

Can't use 'defined(%hash)' (Maybe you should just omit the defined()?) at -e
	line 1 (#1)
    (F) defined() is not usually right on hashes.

    Although defined %hash is false on a plain not-yet-used hash, it
    becomes true in several non-obvious circumstances, including iterators,
    weak references, stash names, even remaining true after undef %hash.
    These things make defined %hash fairly useless in practice, so it now
    generates a fatal error.

    If a check for non-empty is what you wanted then just put it in boolean
    context (see "Scalar values" in perldata):

        if (%hash) {
           # not empty
        }

    If you had defined %Foo::Bar::QUUX to check whether such a package
    variable exists then that's never really been reliable, and isn't
    a good way to enquire about the features of a package, or whether
    it's loaded, etc.

Uncaught exception from user code:
	Can't use 'defined(%hash)' (Maybe you should just omit the defined()?) at -e line 1.