If you look at the tests in the distribution, they don't even test ``find'' with supplied key/value pairs, per what OP wants to do. For example:

 my $some_users = $users->find({"name" => "Joe"});

If you try this, you'll get undefined values as you iterate over the cursor.

(example taken straight from the documentation of MongoDB::Tutorial)

OTOH, if you try this:

my $john = $users->find({"name" => qr/joh?n/i});

It seems to work. (Also from the documentation.)