@Nullable
        @Override
        public String service() {
            final RpcRequest rpcRequest = ctx.rpcRequest();
            if (rpcRequest == null) {
                return null;
            }
            return rpcRequest.serviceName();
        }
Wraps {@link ServiceRequestContext} in an {@link brave.rpc.RpcServerRequest}, for use in
{@link RpcServerHandler}.
brave/brave6/src/main/java/com/linecorp/armeria/server/brave/RpcServiceRequestContextAdapter.java