code: public MultipartContent setContentParts(Collection<? extends HttpContent> contentParts) {
      this.parts = new ArrayList<Part>(contentParts.size());
      for (HttpContent contentPart : contentParts) {
        addPart(new Part(contentPart));
      }
      return this;
    }
docs: Sets the HTTP content parts of the HTTP multipart request, where each part is assumed to have
  no HTTP headers and no encoding.
  
  <p>Overriding is only supported for the purpose of calling the super implementation and
  changing the return type, but nothing else.