@CanIgnoreReturnValue
  public Caffeine<K, V> softValues() {
    requireState(valueStrength == null, "Value strength was already set to %s", valueStrength);
    valueStrength = Strength.SOFT;
    return this;
  }
@Test
  public void softValues() {
    var cache = Caffeine.newBuilder().softValues().build();
    assertThat(cache).isNotNull();
  }