.build();
    cache.put(1, 2);

    // explicitly remove the existing value
    cache.asMap().computeIfPresent(1, (key, value) -> null);
    assertThat(notifications).hasSize(1);
    CacheTesting.checkEmpty(cache);

    // ensure no zombie entry remains
    cache.asMap().computeIfPresent(1, (key, value) -> null);
    assertThat(notifications).hasSize(1);
    CacheTesting.checkEmpty(cache);
  }

    assertThrows(
        UnsupportedOperationException.class, () -> unmod.computeIfAbsent(3, k -> k + "three"));
    assertThrows(UnsupportedOperationException.class, () -> unmod.computeIfPresent(4, (k, v) -> v));
    assertThrows(UnsupportedOperationException.class, () -> unmod.compute(4, (k, v) -> v));
    assertThrows(UnsupportedOperationException.class, () -> unmod.merge(4, "four", (k, v) -> v));

        K key, java.util.function.Function<? super K, ? extends V> mappingFunction) {
      throw new UnsupportedOperationException();
    }

    @Override
    public @Nullable V computeIfPresent(
        K key, BiFunction<? super K, ? super @NonNull V, ? extends @Nullable V> remappingFunction) {
      throw new UnsupportedOperationException();
    }

    @Override
    public @Nullable V compute(

    checkNotNull(key);
    checkNotNull(function);
    return compute(key, (k, oldValue) -> (oldValue == null) ? function.apply(key) : oldValue);
  }

  @Override
  public @Nullable V computeIfPresent(
      K key, BiFunction<? super K, ? super V, ? extends @Nullable V> function) {
    checkNotNull(key);
    checkNotNull(function);