private boolean isMultipartFileCollection(Object object) {
    if (!(object instanceof Iterable)) {
      return false;
    }
    val iterable = (Iterable<?>) object;
    val iterator = iterable.iterator();
    return iterator.hasNext() && iterator.next() instanceof MultipartFile;
  }
Constructor with specified delegate encoder.

@param delegate delegate encoder, if this encoder couldn't encode object.
form-spring/src/main/java/feign/form/spring/SpringFormEncoder.java