CollectionField->setEntrytostringMethod() fails when creating prototype (value is NULL)

[xenatis]

Description:
Bug when using setEntrytoStringMethod on a CollectionField.

In the Twig block collection_entry_row (form_theme.html.twig), when generating the prototype, the parameter value is NULL.

How to reproduce:

        yield CollectionField::new('recipes')
        ->setEntryToStringMethod(fn():string => 'Test') //OK
        ->setEntryToStringMethod('getName') //Error
        ->setEntrytostringMethod(fn(Recipe $recipe):string => $recipe->getName().' test') // Error

Solution:
In the method representAsString (EasyAdminTwigExtension.php) the test on a NULL value should be at the beginning of the method.