private static <I extends Request, O extends Response, U extends Client<I, O>>
    O pushAndExecute(U delegate, ClientRequestContext ctx, I req) throws Exception {
        try (SafeCloseable ignored = ctx.push()) {
            return delegate.execute(ctx, req);
        }
    }
An undefined {@link URI} to create {@link WebClient} without specifying {@link URI}.
core/src/main/java/com/linecorp/armeria/internal/client/ClientUtil.java