Laravel: How To Check If Data In Datatables Is Valid Or Not?

I am trying to get a data from another table through foreign key, i want to check if that data is valid or not, i mean is it empty or not.

for example if the foreing key data is empty, i want to return the null.

here is what i tried to get it right but not nothing works fine if the foreign key is empty.

and here is the relationship between the two tables

 public function driver()
{
    return $this->belongsTo(Driver::class, 'Driver_id');
}

And again i want to clear my point i want to check if the foreign key data is empty or not, if empty i want return null.

Just check if the Driver_id is set.

$driverName = null;
if(isset($bus->Driver_id) && $bus->driver && $bus->driver->first_name) $driverName = $bus->driver->first_name.' '.$bus->driver->last_name.' '.$bus->driver->third_name;
return $driverName;