Laravel MongoDB delete EmbedOne relation

My Model:

use MongoDB\Laravel\Eloquent\Model;
use MongoDB\Laravel\Relations\EmbedsOne;

class TextContent extends Model {
    public function lock(): EmbedsOne
    {
        return $this->embedsOne (TextLock::class);
    }
}


class TextLock extends Model
{
}

This is how store a TextLock:

$lock = new TextLock();
$textContent->lock()->associate ($lock);
$textContent->save();

But I cannot delete it. I tried these methods:

$textContent->lock->delete();
$textContent->save();
// not working, $textContent->lock is still present
// weirdly: $textContent->lock has new prop named 'lock' after this operation. So we have $textContent->lock is `{lock: null}`

$textContent->lock()->delete();
// results in error: MongoDB\Laravel\Relations\EmbedsOne::delete(): Return value must be of type int, true returned

$textContent->lock = null;
$textContent->save();
// not working, $textContent->lock is still present

Any ideas?
I'm using this package: https://github.com/mongodb/laravel-mongodb