Method computeIfAbsent

guava/src/com/google/common/cache/LocalCache.java:4233–4238

(K key, Function<? super K, ? extends V> function)

  }

  @Override
  public V computeIfAbsent(K key, Function<? super K, ? extends V> function) {
    checkNotNull(key);
    checkNotNull(function);
    return compute(key, (k, oldValue) -> (oldValue == null) ? function.apply(key) : oldValue);
  }

  @Override
  public @Nullable V computeIfPresent(