PHP8.1 deprecation: str_replace(): Passing null to parameter #3

Problem/Motivation

I tried to find related issues in the meta #3220021: [meta] Ensure compatibility of Drupal 9 with PHP 8.1 (as it evolves) but failed, sorry if this is a duplicate.
I'm upgrading an inherited project into PHP8.1 and I'm seeing deprecation messages such as

Deprecated function: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in Drupal\filter\Element\ProcessedText::preRenderText() (line 101 of core/modules/filter/src/Element/ProcessedText.php).

Steps to reproduce

• Create a render array of type '#processed_text' where the text value is NULL:

$build = [
   '#type' => 'processed_text',
  '#text' => NULL,
  '#format' => 'filtered_html',
];

Proposed resolution

This is an instance of PHP 8.1: Passing null to non-nullable internal function parameters is deprecated and if we were to use string casting null is always converted to an empty string.
To ensure #text is always treated as a string while preserving error visibility if it’s not set, the following change is recommended:

$text = (string) $element['#text'];

For an example of why this is preferable, see this demonstration.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet