Ancestor { S mostRecent() { return historyChain.getNonnullPayload(0); } private  Ancestor(double logProbability,
      HistoryChain<S> historyChain,
      @Nullable BiFunction<S, S, Bigram<S>> bigramProvider);   }
@Test void testMostRecent() { Ancestor<String> ancestor = Ancestor.createInitial(Ngram::create, "1", "2", "3", null); assertEquals(ancestor.mostRecent(), "3"); }