void appendSuffix(StringBuilder b) {
            b.append(',');
            b.append(missingPolicy.getName());
            if (missingPolicy == MissingPolicy.AS) {
                b.append(",");
                appendMissingValue(b);
            }
            b.append(')');
        }
Returns the serial form of this which contains all information needed to reconstruct this sorter
container-search/src/main/java/com/yahoo/search/query/Sorting.java