code: @Override
    public IdentityLinkEntity involveUser(ExecutionEntity executionEntity, String userId, String type) {
      for (IdentityLinkEntity identityLink : executionEntity.getIdentityLinks()) {
        if (identityLink.isUser() && identityLink.getUserId().equals(userId)) {
          return identityLink;
        }
      }
      return addIdentityLink(executionEntity, userId, null, type);
    }
docs: Adds an IdentityLink for the given user id with the specified type,
  but only if the user is not associated with the execution entity yet.