code: public UrlChain hash(Object hashOnUrl) {
          final String argTitle = "hashOnUrl";
          assertArgumentNotNull(argTitle, hashOnUrl);
          checkWrongUrlChainUse(argTitle, hashOnUrl);
          this.hashOnUrl = hashOnUrl;
          return this;
      }
docs: Set up hash on URL as URL chain.
  The name and specification of this method is synchronized with hash().
  @param hashOnUrl The value of hash on URL. (NotNull)
  @return The created instance of URL chain. (NotNull)