doc bug？

[startjava]

https://vuejs.org/guide/essentials/template-syntax.html#dynamic-argument-value-constraints

Dynamic Argument Value Constraints​
Dynamic arguments are expected to evaluate to a string, with the exception of null. The special value null can be used to explicitly remove the binding. Any other non-string value will trigger a warning.

my html code：

<title>Title</title>

网址1
网址2
网址3

<script type="module" src="directives_4.js"></script>

my js code：
import {createApp} from 'vue'

createApp({
setup() {
let url = "http://www.baidu.com";
let attributename1 = "href";
let attributename2 = null;
let attributename3 = true;

    return {
        url,
        attributename1,
        attributename2,
        attributename3
    }
}

}).mount("#mydiv");

run result F12 no warning ！

but doc say has warning , doc bug?