default <S1 extends Suggestion> @NonNull SuggestionMapper<S1> then(final @NonNull SuggestionMapper<S1> mapper) {
        requireNonNull(mapper, "mapper");
        return suggestion -> mapper.map(this.map(suggestion));
    }
Returns a suggestion mapper that invokes this mapper first and then the provided one.

@param mapper suggestion mapper
@param <S1> mapped suggestion type
@return new mapper
cloud-core/src/main/java/org/incendo/cloud/suggestion/SuggestionMapper.java