static WebClientBuilder builder(SessionProtocol protocol, EndpointGroup endpointGroup) {
        requireNonNull(protocol, "protocol");
        requireNonNull(endpointGroup, "endpointGroup");
        return new WebClientBuilder(protocol, endpointGroup, null);
    }
Returns a new {@link WebClientBuilder} created with the specified {@link SessionProtocol}
and base {@link EndpointGroup}.

@throws IllegalArgumentException if the {@code protocol} is not one of the values in
                                 {@link SessionProtocol#httpValues()} or
                                 {@link SessionProtocol#httpsValues()}.
core/src/main/java/com/linecorp/armeria/client/WebClient.java