if (obj instanceof NullsBefore) {
        NullsBefore other = (NullsBefore) obj;
        return justAfterNull.equals(other.justAfterNull);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return justAfterNull.hashCode();
    }
  }

  public static final class NullsBeforeB extends NullsBefore {