protected $appends = ['profile_thumbnail','thumbnail'];

public function getProfileThumbnailAttribute()
{
    //Check if media has collection and return default.jpg if false
    if ($this->media->isEmpty()) {
        return 'default.jpg';
    } else {
        return $this->media->first()->getUrl('profile_thumbnail');
    }  
}

public function getThumbnailAttribute()
{
    //Check if media has collection and return default.jpg if false
    if ($this->media->isEmpty()) {
        return 'default.jpg';
    } else {
        return $this->media->first()->getUrl('thumbnail');
    }  
}