How do I validate non-required fields?

[eluser]sv3tli0[/eluser]
@Skyscraper

Form validation is validating you last_name as correct empty string - '' and pass it to your update function..
This work can't be skipped because Validation has validated both first and last name as correct (emtpy or not) and pass them to update which do them both..
You may set at update function a loop..

Code:

foreach($inputs as $key=>$value){
   if(empty($value)){
       unset($inputs[$key]);
   }
}

which will skip all empty fields..