Source must be selected

// elseif (is_string($value['target_id']) && isset($source_value['target_id']) && $value['target_id'] === $source_value['target_id']) {
// $source_valid = TRUE;
// }
elseif (is_array($value) && is_array($source_value) && isset($value['target_id'], $source_value['target_id']) && $value['target_id'] === $source_value['target_id']) {
$source_valid = TRUE;
}

Seems there's no details here?