1. Take any weapon and several magazines for it.
2. Reload it and run

player addMagazine [(primaryWeaponMagazine player) select 0, 0];

in debug window.

3. Check magazines count with

hint str (magazinesAmmo player);

Magazines with zero ammo count will be ignored.
Check ammo with

hint str(soldiermagazines player);

You will see magazines with zero ammo count.

So you cannot check if unit has any empty magazines and cannot get classnames.