I did everything but with empty "function configureFields()" in CommentCrudController.php I've got an error while trying to add a new comment:

An exception occurred while executing a query: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'conference_id' cannot be null

I've noticed that there was no field "conference name" in a comment creation form and understood that it is about connection with Conference field.
So I solved it with adding function configureFields with code from symfony doc:

public function configureFields(string $pageName): iterable
{
return [
IdField::new('id')->onlyOnIndex(),
Field::new('author'),
TextareaField::new('text'),
EmailField::new('email'),
DateTimeField::new('createdAt'),
AssociationField::new('conference'),
];
}

and it works.

Please tell me, maybe it was another way because I'm new to symfony.