public Comparator<T> get(final String fieldId, final boolean ignoreCase) {
            Objects.requireNonNull(fieldId);
            return NullSafe.get(comparatorMap.get(fieldId),
                    caseAwareComparator -> caseAwareComparator.get(ignoreCase));
        }
Gets the comparator associated with fieldId. If the field in question
has string values then ignoreCase will determine whether a case-sensitive
or case-insensitive comprator is returned.

@param fieldId    The ID of the field.
@param ignoreCase Whether case should be ignored in comparisons of string values.
@return The comparator or null if fieldId is not found in the map.
stroom-util-shared/src/main/java/stroom/util/shared/CompareUtil.java