code: private static Optional<ICondition> asContainsAll( JsonObject json)
      {
      return
        json.containsKey( HAS_ALL_KEY)
        ? Optional.of( new ContainsAll( toIdentifiers( json.getJsonArray( HAS_ALL_KEY))))
        : Optional.empty();
      }
docs: Returns the ContainsAll condition represented by the given JSON object or an empty
  value if no such condition is found.