Criteria on editing entity associtation field in EasyAdmin

Question

I am using EasyAdmin4 in my project.

What I want to achieve is my associated field should be disabled only on edit and only if it is not null.

I could disable it in the configuration:

public function configureFields(string $pageName): iterable
{
    $fields = parent::configureFields($pageName);

    $learningPathField = AssociationField::new('LearningPath');
    if ($pageName === Action::NEW) {
        $learningPathField->setHelp('Warning! Once you set this, you can not change when you edit Learning Path!');
    }
    if ($pageName === Action::EDIT) {
        $learningPathField->setDisabled(true);
    }
    $fields[] = $learningPathField;
    return $fields;
}

But I'd like to set $learningPathField->setDisabled(true); only its value is not null.

How can I get the value of this field?