Implicitly marking parameter $entity as nullable is deprecated

Problem/Motivation

In PHP 8.4 it is deprecated to add a default value of a parameter as NULL, but not making it nullable.

Steps to reproduce

Try to run the module with PHP 8.4.

Proposed resolution

Mark the parameter as accepting null.

Remaining tasks

Add type declarations to the other methods as well ?

User interface changes

none

API changes

n/a

Data model changes

n/a