How to fix new stdClass error - php

Question

I am trying to understand the new stdClass in terms of sending data to a function, I've created the following code and I'll get an error that's saying Warning: Creating default object from empty value, however, still I get the json data as well. How to fix the error and why I am getting it?
$send = new stdClass();
$send->user->id = '12121212121';
$send->message->attachment->type = 'file';
$send->message->attachment->image = 'png';
$res = process($send);
function process($send){
$data = json_encode($send);
print_r($data);
}
Result is looks like this and there is an error above below result as I mentioned it:
{"user":{"id":"12121212121"},"message":{"attachment":{"type":"file","image":"png"}}}

Answer 1

Create stdClass for each reference like this
$send = new stdClass();
$send->user=new stdClass();
$send->user->id = '12121212121';
$send->message=new stdClass();
$send->message->attachment=new stdClass();
$send->message->attachment->type = 'file';
$send->message->attachment->image = 'png';
$res = process($send);
function process($send){
$data = json_encode($send);
print_r($data);
}