code: private static void toHttp2HeadersFilterTE(Entry<CharSequence, CharSequence> entry,
                                                 HttpHeaders out) {
          if (AsciiString.indexOf(entry.getValue(), ',', 0) == -1) {
              if (AsciiString.contentEqualsIgnoreCase(AsciiString.trim(entry.getValue()),
                                                      HttpHeaderValues.TRAILERS)) {
                  out.add(HttpHeaderNames.TE, HttpHeaderValues.TRAILERS.toString());
              }
          } else {
              final List<CharSequence> teValues = StringUtil.unescapeCsvFields(entry.getValue());
              for (CharSequence teValue : teValues) {
                  if (AsciiString.contentEqualsIgnoreCase(AsciiString.trim(teValue),
                                                          HttpHeaderValues.TRAILERS)) {
                      out.add(HttpHeaderNames.TE, HttpHeaderValues.TRAILERS.toString());
                      break;
                  }
              }
          }
      }
docs: Filter the {@link HttpHeaderNames#TE} header according to the
  <a href="https://tools.ietf.org/html/rfc7540#section-8.1.2.2">special rules in the HTTP/2 RFC</a>.
  @param entry An entry whose name is {@link HttpHeaderNames#TE}.
  @param out the resulting HTTP/2 headers.