ImmutableSet<N> validated = validate(startNodes);
    return () -> newTraversal().postOrder(validated.iterator());
  }

  abstract Traversal<N> newTraversal();

  @SuppressWarnings("CheckReturnValue")
  private ImmutableSet<N> validate(Iterable<? extends N> startNodes) {
    ImmutableSet<N> copy = ImmutableSet.copyOf(startNodes);
    for (N node : copy) {

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.errorprone.annotations.CheckReturnValue;
import com.google.errorprone.annotations.ForOverride;
import com.google.errorprone.annotations.InlineMe;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.RetainedWith;

      return Optional.of((long) length);
    }

    @Override
    public byte[] read() {
      return Arrays.copyOfRange(bytes, offset, offset + length);
    }

    @SuppressWarnings("CheckReturnValue") // it doesn't matter what processBytes returns here
    @Override
    @ParametricNullness
    public <T extends @Nullable Object> T read(ByteProcessor<T> processor) throws IOException {

@com.google.errorprone.annotations.CheckReturnValue

@com.google.errorprone.annotations.CheckReturnValue

@com.google.errorprone.annotations.CheckReturnValue

import org.jspecify.annotations.Nullable;

/**
 * Unit test for {@link NullPointerTester}.
 *
 * @author Kevin Bourrillion
 * @author Mick Killianey
 */
@SuppressWarnings({
  "CheckReturnValue",
  "unused", // many methods tested reflectively -- maybe prefer local @Keep annotations?
})
@NullUnmarked
public class NullPointerTesterTest extends TestCase {

  /** Non-NPE RuntimeException. */

@com.google.errorprone.annotations.CheckReturnValue

@com.google.errorprone.annotations.CheckReturnValue

@com.google.errorprone.annotations.CheckReturnValue