PHP warnings when using xml format

[Chi-teck]

Describe the bug That happens when running commands that returns RowsOfFields in XML format.

[warning] foreach() argument must be of type array|object, null given XmlSchema.php:39

To Reproduce drush pml --format=xml

System Configuration

Q	A
Drush version?	11.x
Drupal version?	9.x
PHP version	8.x
OS?	Linux

[Chi-teck]

The issue still exists in 12.x.