import java.util.stream.Collectors;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * GWT emulated version of {@link com.google.common.collect.ImmutableSortedMap}. It's a thin wrapper
 * around a {@link java.util.TreeMap}.
 *
 * @author Hayward Chan
 */
@ElementTypesAreNonnullByDefault
public final class ImmutableSortedMap<K, V> extends ForwardingImmutableMap<K, V>