Method computeIfPresent

guava/src/com/google/common/cache/LocalCache.java:4240–4246

(
      K key, BiFunction<? super K, ? super V, ? extends @Nullable V> function)

  }

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

  @Override
  public @Nullable V merge(