Warn users in SeriesAggreg when ConvertFun is not provided
It may be a good idea to return a message when SeriesAggreg() is applied on a unknown object (e.g. not InputsModel or OutputsModel objects) and ConvertFun is also not provided.
It may be a good idea to return a message when SeriesAggreg() is applied on a unknown object (e.g. not InputsModel or OutputsModel objects) and ConvertFun is also not provided.