code: public <T extends OmiseObject> T returns(Class<T> klass) throws IOException, OmiseException {
          InputStream stream = preprocess(roundtrip());
          if (stream == null) {
              return null;
          }
  
          try {
              return serializer.deserialize(stream, klass);
          } finally {
              stream.close();
          }
      }
docs: Executes the operation using the parent {@link Resource}'s {@link OkHttpClient},
  sending any given {@link Params} and automatically deserializes the result into
  an instance of the given class.
  
  @param klass The {@link Class} of the result.
  @param <T>   The type of the result to return.
  @return An instance of the type T deserialized from the response body.
  @throws IOException    when encountering general network communications problem.
  @throws OmiseException when receiving an error object from the Omise API.