code: public HalResource setLink(String relation, Link link) {
      if (link == null) {
        return this;
      }
      return addResources(HalResourceType.LINKS, relation, false, new Link[] {
          link
      });
    }
docs: Sets link for the given relation. Overwrites existing one. If {@code link} is {@code null} it gets ignored.
  @param relation Link relation
  @param link Link to add
  @return HAL resource