Problems when trying to change frontpages?

// check for a valid image
  if(!$this->source->exists() || $this->source->type() != 'image') {
    throw new Error('The given image is invalid', static::ERROR_INVALID_IMAGE);

  // check for a valid driver
  if(!array_key_exists($this->options['driver'], static::$drivers)) {
    throw new Error('Invalid thumbnail driver', static::ERROR_INVALID_DRIVER);

@Lumega Could you please elaborate a bit more? I’m missing some context and the Kirby version your are referring to.