Error '[PHP Notice #8] Trying to access array offset on value of type null WebserviceOutputBuilder.php

[KhaliMoh]

Hello,

I bought a prestashop module that use API to connect & synchronize Prestashop & Odoo, when i'm trying to synchronize from Odoo end, an error occured (Copy of error : Error '[PHP Notice #8] Trying to access array offset on value of type null (/var/www/html/classes/webservice/WebserviceOutputBuilder.php, line 716)'. When i check with module developer it tell me that it's an error related to Core API of prestashop webservice an it may be related to PHP version, but checking Prestashop documentation all configuration are good 

Prestashop version : 1.7.8.5

PHP : 7.4.28

Can anyone help please on this or help to downgrade PHP from 7.4.28 to 7.4.0 ?

Thanks in advance