encode method
Implementation
@override
void encode(KeyedArchive object) {
  super.encode(object);
  if (description == null) {
    throw ArgumentError(
        "APIResponse must have non-null values for: 'description'.");
  }
  object.encode("description", description);
  object.encodeObjectMap("headers", headers);
  object.encodeObjectMap("content", content);
}