Indstil standardværdier, der ikke er nul, for inputvariablen(erne).
$contact = new Contact;
$contact->name = Input::get('name');
$contact->username = Input::get('username', '');
$contact->save();
Eller i nyere Laravel-versioner:
$contact = new Contact;
$contact->name = $request->input('name');
$contact->username = $request->input('username', '');
$contact->save();