POST-ing a file with WWW::Mechanize

Hello!

When POST-ing files with LWP I could usually specify the field as an 
array ref which looked like this:
/fieldname/ => [/local_filespec/ => /as_what_name/],

Now, I am trying to do the same with WWW::Mech and what I get is Mech 
dying with error:
/Can't call method "value" on an undefined value at WWW/Mechanize.pm 
line 1347./

Any ideas what to associate a field with to POST a file with 
'/as_what_name/' just like in the LWP case?

Using WWW::Mech version 1.30


Thanks,
P.Krumins