}

      this.justAfterNull = justAfterNull;
    }

    @Override
    public int compare(@Nullable String lhs, @Nullable String rhs) {
      if (lhs == rhs) {
        return 0;
      }
      if (lhs == null) {
        // lhs (null) comes just before justAfterNull.
        // If rhs is b, lhs comes first.
        if (rhs.equals(justAfterNull)) {
          return -1;
        }