@Nullable
    static BuiltInProperty findByKey(String key) {
        return keyToEnum.entrySet().stream()
                        .filter(e -> e.getKey().equals(key))
                        .map(Entry::getValue)
                        .findFirst().orElse(null);
    }
{@code "tls.proto"} - the current {@linkplain SSLSession#getProtocol() TLS protocol}.
Unavailable if TLS handshake is not finished or the connection is not a TLS connection, such as
{@code "TLSv1.2"}.
core/src/main/java/com/linecorp/armeria/common/logging/BuiltInProperty.java