$source = isset($config['source_url_field']) ? $config['source_url_field'] : '';
$source_field[$bundle] = isset($config['source_field']) ? $config['source_field'] : $source;
$source = isset($config['source_url_field']) ? $config['source_url_field'] : '';
$source_field[$bundle] = isset($config['source_field']) ? $config['source_field'] : $source;