code: public static Set<String> namesAsString(Headers<CharSequence, CharSequence, ?> headers) {
          return new CharSequenceDelegatingStringSet(headers.names());
      }
docs: {@link Headers#names()} and convert each element of {@link Set} to a {@link String}.
  @param headers the headers to get the names from
  @return a {@link Set} of header values or an empty {@link Set} if no values are found.