docs: public OperationBuilder addFileAsAttachment(final File file) {
          Assert.checkNotNullParam("file", file);
          try {
              FileStreamEntry entry = new FileStreamEntry(file);
              if (inputStreams == null) {
                  inputStreams = new ArrayList<InputStream>();
              }
              inputStreams.add(entry);
          } catch (IOException e) {
              throw new RuntimeException(e);
          }
          return this;
      }