comparator, keyFunction, valueFunction, mergeFunction);
  }

  /*
   * TODO(kevinb): Confirm that ImmutableSortedMap is faster to construct and
   * uses less memory than TreeMap; then say so in the class Javadoc.
   */
  private static final Comparator<?> NATURAL_ORDER = Ordering.natural();

  private static final ImmutableSortedMap<Comparable<?>, Object> NATURAL_EMPTY_MAP =
      new ImmutableSortedMap<>(

	// to the destination metadata.
	sc := r.Header.Get(xhttp.AmzStorageClass)
	if sc == "" {
		sc = r.Form.Get(xhttp.AmzStorageClass)
	}

	// if x-amz-metadata-directive says REPLACE then
	// we extract metadata from the input headers.
	if isDirectiveReplace(r.Header.Get(xhttp.AmzMetadataDirective)) {
		emetadata, err := extractMetadataFromReq(ctx, r)
		if err != nil {
			return nil, err