if (n == 1) {
      // for n=1 we don't create a hash table, but we need to do the checkEntryNotNull check!
      // requireNonNull is safe because the first `2*n` elements have been filled in.
      checkEntryNotNull(
          requireNonNull(alternatingKeysAndValues[keyOffset]),
          requireNonNull(alternatingKeysAndValues[keyOffset ^ 1]));
      return null;
    }