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

mysqli_change_user エントリポイントから開始し、文書化されている NULL の動作と提供された PHP の再現コードを比較します。NULL を渡すことで既存のデータベース選択が維持され、再現コードによって SELECT DATABASE() が引き続き "test" を返すことが確認できれば完了です。