private static Set<String> toDocumentTypeNames(List<NewDocumentType> types) {
        return types.stream()
                .map(type -> type.getFullName().getName())
                .collect(toCollection(LinkedHashSet::new));
    }
Returns any change to the indexing mode of a cluster.

@author hmusum
@author bjorncs
config-model/src/main/java/com/yahoo/vespa/model/application/validation/change/IndexingModeChangeValidator.java