mysqli_change_user does not allow to use NULL for $database param

Description

According to the documentation, the third parameter in mysqli_change_user is nullable (not optional though) and passing NULL should connect to the same database.

If desired, the null value may be passed resulting in only changing the user and not selecting a database. To select a database in this case use the mysqli_select_db() function.

But to my knowledge this was never possible and is still not supported by mysqli. This code will reset database to NULL

$mysqli = new mysqli("localhost", "my_user", "my_password", "test");
$mysqli->change_user("my_user", "my_password", null);
var_dump($mysqli->query("SELECT DATABASE()")->fetch_row()[0]);

Resulted in this output:

NULL

But I expected this output instead:

string(4) "test"

PHP Version

All versions

Operating System

No response

从 mysqli_change_user 入口点开始，将文档所述的 NULL 行为与提供的 PHP 复现进行比较。当传入 NULL 能保留现有数据库选择，并且复现确认 SELECT DATABASE() 仍返回 "test" 时，即表示完成。