public static TrainingStatistics undefined() {
   return new TrainingStatistics(Maybe.<Map<SentenceKey, EnsembleStatistics>>Nothing());
 }
 public SentenceStatistics(Counter<String> relationDistribution) {
   this.confidence = Maybe.Nothing();
   this.relationDistribution = relationDistribution;
 }
 public Maybe<Set<SentenceKey>> getSentenceKeys() {
   if (!impl.isDefined()) return Maybe.Nothing();
   return Maybe.Just(impl.get().keySet());
 }