[D9 PHP 8.1] Deprecated function: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated in text_summary() (line 71 of core/modules/text/text.module)

My website is now with DrupalCore version 9.4.7 and PHP 8.1.

How to reproduce:
when i access to one of my page (views with filter and pagination) with content, the website return theses two error.
Deprecated function: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated in text_summary() (line 71 of core/modules/text/text.module).
And
Deprecated function: mb_strlen(): Passing null to parameter #1 ($string) of type string is deprecated in text_summary() (line 95 of core/modules/text/text.module).

It seems calling the function text_summary() with null params, then the results is in this warning.

Yes! it caused by my custom module, in teaser of node

Indeed, I called the function text_summary() like this :

text_summary($node->get($field_name)->value, NULL, 50);

when i have to call it like this

text_summary($node->get($field_name)->value ?? "", NULL, 50);

then the error!

Now the error is gone!
Thanks for all!