code: public void addFile(InputStream inputStream, String name) {
          fileStreams.put(name, inputStream);
  
          // remove duplicate key
          if (files.containsKey(name)) {
              files.remove(name);
          }
      }
docs: Adds a file to your assembly. If the field name specified already exists, it will override the content of the
  existing name.
  
  @param inputStream {@link InputStream} the file to be uploaded.
  @param name {@link String} the field name of the file when submitted Transloadit.