code: public CacheConfigurationBuilder<K, V> withKeyCopier(Copier<K> keyCopier) {
      return withCopier(new DefaultCopierConfiguration<>(requireNonNull(keyCopier, "Null key copier"), DefaultCopierConfiguration.Type.KEY));
    }
docs: Adds by-value semantic using the provided {@link Copier} for the key on heap.
  <p>
  {@link Copier}s are what enable control of by-reference / by-value semantics for on-heap tier.
  
  @param keyCopier the key copier to use
  @return a new builder with the added key copier