code: @SuppressWarnings("unchecked")
      public List<Link> getLinksBy(final String rel) {
          final String curiedRel = curies.resolve(rel);
          if (this.links.containsKey(curiedRel)) {
              final Object links = this.links.get(curiedRel);
              return links instanceof List
                      ? (List<Link>) links
                      : singletonList((Link)links);
          } else {
              return emptyList();
          }
      }
docs: <p>
  Returns the list of links having the specified link-relation type.
  </p>
  <p>
  If CURIs are used to shorten custom link-relation types, it is possible to either use expanded link-relation types,
  or the CURI of the link-relation type. Using CURIs to retrieve links is not recommended, because it
  requires that the name of the CURI is known by clients.
  </p>
  
  @param rel the link-relation type of the retrieved link.
  @return list of matching link
  
  @see <a href="https://tools.ietf.org/html/draft-kelly-json-hal-08#section-8.2">draft-kelly-json-hal-08#section-8.2</a>
  @since 0.1.0