code: private static Optional<ICondition> asLessThan( JsonObject json)
      {
      return
        Optional.of( json)
        .filter( j -> j.containsKey( LESS_THAN_KEY))
        .map( j -> j.getJsonObject( LESS_THAN_KEY))
        .map( a -> new AssertLess( a.getString( PROPERTY_KEY), a.getInt( MAX_KEY)));
      }
docs: Returns the AssertLess condition represented by the given JSON object or an empty
  value if no such condition is found.