Sets.newLinkedHashSet(Iterables.transform(set, Optional::fromNullable));
      optionalSets.add(optionalSet);
    }
    Set<List<Optional<?>>> cartesianProduct = Sets.cartesianProduct(optionalSets);
    return Iterables.transform(cartesianProduct, objs -> Lists.transform(objs, Optional::orNull));
  }

  private CacheBuilder<Object, Object> createCacheBuilder(
      @Nullable Integer concurrencyLevel,

import java.util.AbstractList;
import java.util.List;
import java.util.ListIterator;
import java.util.RandomAccess;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@link Lists#cartesianProduct(List)}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
final class CartesianList<E> extends AbstractList<List<E>> implements RandomAccess {

  private final transient ImmutableList<List<E>> axes;

import java.util.AbstractList;
import java.util.List;
import java.util.ListIterator;
import java.util.RandomAccess;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@link Lists#cartesianProduct(List)}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
final class CartesianList<E> extends AbstractList<List<E>> implements RandomAccess {

  private final transient ImmutableList<List<E>> axes;