code: public SubmissionLink createSubmissionLink(final Submission submission) {
          Head head = getRoot().find("Head", Head.class);
          if (head == null) {
              head = createHead();
          }
          final SubmissionLink submissionLink =
                  new SubmissionLink(head, "Submission",
                          new ObjectId(submission.getString()));
          head.insert(submissionLink);
          return submissionLink;
      }
docs: Create a link to the submission in the head. If head doesn't already
  exist create it.
  
  @param submission
  the submission to link
  @return the submission link