for k, vv := range trailer {
		lowKey, ascii := http2lowerHeader(k)
		if !ascii {
			// Skip writing invalid headers. Per RFC 7540, Section 8.1.2, header
			// field names have to be ASCII characters (just as in HTTP/1.x).
			continue
		}
		// Transfer-Encoding, etc.. have already been filtered at the
		// start of RoundTrip
		for _, v := range vv {
			cc.writeHeader(lowKey, v)
		}
	}