code: public Converter<?, NetworkRequest> requestConverter(Type type, Annotation[] annotations) {
          checkNotNull(type, "type == null");
          checkNotNull(annotations, "annotations == null");
  
          for (int i = 0, count = converters.size(); i < count; i++) {
              Converter<?, NetworkRequest> converter =
                      converters.get(i).toRequest(type, annotations);
              if (converter != null) {
                  return converter;
              }
          }
  
          StringBuilder builder = new StringBuilder("Could not locate Request converter for ")
                  .append(type)
                  .append(". Tried:");
          for (Factory converterFactory : converters) {
              builder.append("\n * ").append(converterFactory.getClass().getName());
          }
          throw new IllegalArgumentException(builder.toString());
      }
docs: Returns a {@link Converter} for {@code type} to {@link NetworkRequest} from the available
  {@linkplain #converterFactories() factories}.