public static <T_ROW> FilterFieldMappers<T_ROW> of(final Collection<FilterFieldMapper<T_ROW>> fieldMappers) {

        return new FilterFieldMappers<>(Optional.ofNullable(fieldMappers)
                .map(fieldMappers2 -> fieldMappers2.stream()
                        .collect(Collectors.toMap(
                                fieldMapper -> fieldMapper.getFieldDefinition().getFilterQualifier().toLowerCase(),
                                Function.identity())))
                .orElseGet(Collections::emptyMap));
    }
A wrapper for a collection of {@link FilterFieldMapper<T_ROW>}
stroom-util/src/main/java/stroom/util/filter/FilterFieldMappers.java