ExtractValue extracts a BigDecimal and handles scale (well it doesn't yet, but maybe in the future). I think it would be an integer overload of this method actually. 
For now I think it does not necessarily have to be in the command base class, as there is no other command class that encodes / decodes integers like that, but I can envision that there will be in the future, so in the command base class is fine as well.