Fix ssh_keys template 'group cannot be determined' error

I had some trouble using the 'ssh_keys' attribute when using the users cookbook...
When my user.json did NOT include a 'gid' attribute, I was getting an error:

template[/home/giorgos/.ssh/authorized_keys] (/tmp/vagrant-chef-3/chef-solo-1/cookbooks/users/providers/manage.rb line 121) had an error: Chef::Exceptions::GroupIDNotFound: cannot determine group id for 'giorgos', does the group exist on this system?

(https://github.com/opscode-cookbooks/users/blob/master/providers/manage.rb#L121)

The template resource was not able to find the group id...
So, I tried including a 'gid' attribute, only this time:

==> default: Chef::Exceptions::User
==> default: ----------------------
==> default: user[giorgos] (/tmp/vagrant-chef-3/chef-solo-1/cookbooks/users/providers/manage.rb line 94) had an error: Chef::Exceptions::User: Couldn't lookup integer GID for group name 7000

...leaving me no choice but to change the source code...
(This is all on an OpenSUSE 13.1 VM, so it might work on other OS)