@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class AbstractSequentialIterator<T> extends UnmodifiableIterator<T> {
  @CheckForNull private T nextOrNull;

  /**
   * Creates a new iterator with the given first element, or, if {@code firstOrNull} is null,
   * creates a new empty iterator.
   */
  protected AbstractSequentialIterator(@CheckForNull T firstOrNull) {
    this.nextOrNull = firstOrNull;
  }

  /**

@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class AbstractSequentialIterator<T> extends UnmodifiableIterator<T> {
  @CheckForNull private T nextOrNull;

  /**
   * Creates a new iterator with the given first element, or, if {@code firstOrNull} is null,
   * creates a new empty iterator.
   */
  protected AbstractSequentialIterator(@CheckForNull T firstOrNull) {
    this.nextOrNull = firstOrNull;
  }

  /**