static RpcRequest of(Class<?> serviceType, String method, @Nullable Object parameter) {
        final List<Object> parameters = parameter == null ? SINGLE_NULL_PARAM
                                                          : ImmutableList.of(parameter);
        return new DefaultRpcRequest(serviceType, null, method, parameters);
    }
Creates a new instance with a single parameter.
core/src/main/java/com/linecorp/armeria/common/RpcRequest.java