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