Gedmo\Tree test: SQLite fails, MySQL passes

In a simple test of a Category tree using SQLite, the test fails during setup with

AppBundle\Tests\Entity\CategoryTest::testSetProductCategory() Doctrine\DBAL\DBALException: An exception occurred while executing 'INSERT INTO category (title, lft, lvl, rgt, root, deletedAt, parent_id) VALUES (?, ?, ?, ?, ?, ?, ?)' with params ["Hook", null, null, null, null, null, null]: SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: category.lft

Performing the same test with a MySQL database the test succeeds. Test environment databases & schemas are created with console commands.

test setup:

public function setUp()
{
    self::bootKernel();
    $this->em = static::$kernel->getContainer()
            ->get('doctrine')
            ->getManager()
    ;
    $product = new \AppBundle\Entity\Product();
    $product->setName('foo');
    $this->em->persist($product);

    $cat = new \AppBundle\Entity\Category();
    $cat->setTitle('Hook');
    $this->em->persist($cat);

    $child = new \AppBundle\Entity\Category();
    $child->setTitle('Dry');
    $child->setParent($cat);
    $this->em->persist($child);

    $this->em->flush();
}

config_test.yml with SQLite:

doctrine:
    dbal:
        default_connection: test
        connections:
            test:
                driver:   pdo_sqlite
                path:     %kernel.cache_dir%/test.sqlite

config_test.yml with MySQL:

doctrine:
    dbal:
        host:     localhost
        dbname:   flyby_test
        user:     root
        password: [password]