presto-main/src/main/java/io/prestosql/sql/planner/planprinter/IoPlanPrinter.java/IoPlanPrinter/formatMarker
class IoPlanPrinter:        private FormattedMarker formatMarker(Marker marker)
        {
            if (!marker.getValueBlock().isPresent()) {
                return new FormattedMarker(Optional.empty(), marker.getBound());
            }
            return new FormattedMarker(Optional.of(valuePrinter.castToVarcharOrFail(marker.getType(), marker.getValue())), marker.getBound());
        }