Doctrine does not want to assign `null` to boolean property

I have a new Symfony 7 application, that supports user accounts. The basic setup for this is very straightforward:

symfony new mimesia --version="7.1.*" --webapp
php bin/console make:user

The application has to talk to an existing database, which is mostly compatible with the scheme Symfony uses. However, the verified column of the existing data is called verified, rather than is_verified, and it can be NULL.

Solving this discrepancy should be easy enough, so I just extended the Doctrine annotations in Entity/User like so:

#[ORMColumn(name: 'verified', type: 'boolean', nullable: true)]
private bool $isVerified = false;

When I try to run the application, it runs into a server error:

Cannot assign null to property AppEntityUser::$isVerified of type bool

This makes no sense to me, because the nullable flag should have taken care of that. Is this a bug in the libraries, or am I missing something? Either way, how can we fix this?