Doctrine Sluggable - Column 'slug' cannot be null

I am using Doctrine, with DoctrineExtensions via StofDoctrineExtensionsBundle to generate slugs automatically using "Doctrine Extensions Sluggable" behavior.

The listener seems to be registred properly. Entity field is also marked as sluggable.

When trying to persist my entity via Symfony form, slug generation does not happen. Database exception is being thrown.

Exception:

An exception occurred while executing 'INSERT INTO event (startDate, endDate, title, slug, description, image, followers, city, place) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)' with params ["2017-06-24 20:00:00", "2017-06-26 12:00:00", "Test event name for slug generation", null, "Test", null, null, "Somewhere", "Somewhere else"]:

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'slug' cannot be null

Versions:

PHP                                  7.0.15
symfony/symfony                      v3.2.9
doctrine/doctrine-bundle             1.6.8
doctrine/orm                         v2.5.6
gedmo/doctrine-extensions            v2.4.29
stof/doctrine-extensions-bundle      v1.2.2 

config.yml

doctrine:
    dbal:
        driver: pdo_mysql
        host: '%database_host%'
        port: '%database_port%'
        dbname: '%database_name%'
        user: '%database_user%'
        password: '%database_password%'
        charset: UTF8
    orm:
        auto_generate_proxy_classes: '%kernel.debug%'
        naming_strategy: doctrine.orm.naming_strategy.underscore
        auto_mapping: true

stof_doctrine_extensions:
    default_locale: '%locale%' # pl
    translation_fallback: true
    orm:
        default:
            sluggable: true

Entity (Event.orm.xml)

<?xml version="1.0" encoding="utf-8"?>
<doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping http://doctrine-project.org/schemas/orm/doctrine-mapping.xsd"
                  xmlns:gedmo="http://Atlantic18.github.io/DoctrineExtensions/schemas/orm/doctrine-extensions-3.0.xsd">
    <entity repository-class="AppBundle\Repository\EventRepository" name="AppBundle\Entity\Event">
        <id name="id" type="integer" column="id">
            <generator strategy="AUTO"/>
        </id>
        <field name="startDate" type="datetime" column="startDate"/>
        <field name="endDate" type="datetime" column="endDate"/>
        <field name="title" type="string" column="title" length="255"/>
        <field name="slug" type="string" column="slug" length="255" unique="true">
            <gedmo:slug unique="true" updatable="true" fields="title" separator="-" />
        </field>
        <field name="description" type="text" column="description" nullable="true"/>
        <field name="image" type="string" column="image" length="255" nullable="true"/>
        <field name="followers" type="integer" column="followers" nullable="true"/>
        <field name="city" type="string" column="city" nullable="false" />
        <field name="place" type="string" column="place" nullable="true" />
    </entity>
</doctrine-mapping>

Controller action:

    public function createAction(Request $request)
    {
        $form = $this->createForm(EventType::class);

        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            /** @var Event $event */
            $event = $form->getData();

            $em = $this->getDoctrine()->getManager();
            $em->persist($event);
            $em->flush();

            $this->addFlash('success', 'event created');
            return $this->redirectToRoute('calendar_event', [
                'slug' => $event->getSlug()
            ]);
        }

        return ['form' => $form->createView()];
    }

Full stack trace:

[1] Doctrine\DBAL\Exception\NotNullConstraintViolationException: An exception occurred while executing 'INSERT INTO event (startDate, endDate, title, slug, description, image, followers, city, place) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)' with params ["2017-06-24 20:00:00", "2017-06-26 12:00:00", "Test event name for slug generation", null, "Test", null, null, "Somewhere", "Somewhere else"]:

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'slug' cannot be null
    at n/a
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php line 112

    at Doctrine\DBAL\Driver\AbstractMySQLDriver->convertException('An exception occurred while executing \'INSERT INTO event (startDate, endDate, title, slug, description, image, followers, city, place) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)\' with params ["2017-06-24 20:00:00", "2017-06-26 12:00:00", "Test event name for slug generation", null, "Test", null, null, "Somewhere", "Somewhere else"]:SQLSTATE[23000]: Integrity constraint violation: 1048 Column \'slug\' cannot be null', object(PDOException))
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/DBALException.php line 128

    at Doctrine\DBAL\DBALException::driverExceptionDuringQuery(object(Driver), object(PDOException), 'INSERT INTO event (startDate, endDate, title, slug, description, image, followers, city, place) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)', array('2017-06-24 20:00:00', '2017-06-26 12:00:00', 'Test event name for slug generation', null, 'Test', null, null, 'Somewhere', 'Somewhere else'))
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/Statement.php line 177

    at Doctrine\DBAL\Statement->execute()
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php line 281

    at Doctrine\ORM\Persisters\Entity\BasicEntityPersister->executeInserts()
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 1014

    at Doctrine\ORM\UnitOfWork->executeInserts(object(ClassMetadata))
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 378

    at Doctrine\ORM\UnitOfWork->commit(null)
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/EntityManager.php line 356

    at Doctrine\ORM\EntityManager->flush(null)
        in /project_home/var/cache/dev/appDevDebugProjectContainer.php line 7072

    at DoctrineORMEntityManager_00000000751279ee000000007e7efeea3473a0393d6fcd1415b2fc588e376308->flush(null)
        in /project_home/var/cache/dev/jms_diextra/doctrine/EntityManager_59394e2cc7d86.php line 313

    at EntityManager59394e2cc7d86_546a8d27f194334ee012bfe64f629947b07e4919\__CG__\Doctrine\ORM\EntityManager->flush()
        in /project_home/src/AppBundle/Controller/CalendarController.php line 56

    at AppBundle\Controller\CalendarController->createAction(object(Request))
        in  line 

    at ReflectionMethod->invokeArgs(object(CalendarController), array(object(Request)))
        in /project_home/vendor/jms/cg/src/CG/Proxy/MethodInvocation.php line 84

    at CG\Proxy\MethodInvocation->proceed()
        in /project_home/vendor/jms/security-extra-bundle/Security/Authorization/Interception/MethodSecurityInterceptor.php line 133

    at JMS\SecurityExtraBundle\Security\Authorization\Interception\MethodSecurityInterceptor->intercept(object(MethodInvocation))
        in /project_home/vendor/jms/cg/src/CG/Proxy/MethodInvocation.php line 79

    at CG\Proxy\MethodInvocation->proceed()
        in /project_home/var/cache/dev/jms_diextra/proxies/AppBundle-Controller-CalendarController.php line 21

    at EnhancedProxye0ff800f_2852d4e43776e45f00f38751350397dbf530e575\__CG__\AppBundle\Controller\CalendarController->createAction(object(Request))
        in  line 

    at call_user_func_array(array(object(CalendarController), 'createAction'), array(object(Request)))
        in /project_home/var/cache/dev/classes.php line 4228

    at Symfony\Component\HttpKernel\HttpKernel->handleRaw(object(Request), 1)
        in /project_home/var/cache/dev/classes.php line 4183

    at Symfony\Component\HttpKernel\HttpKernel->handle(object(Request), 1, true)
        in /project_home/vendor/symfony/symfony/src/Symfony/Component/HttpKernel/Kernel.php line 168

    at Symfony\Component\HttpKernel\Kernel->handle(object(Request))
        in /project_home/web/app_dev.php line 28

    at require('/project_home/web/app_dev.php')
        in /project_home/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Resources/config/router_dev.php line 40

[2] Doctrine\DBAL\Driver\PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'slug' cannot be null
    at n/a
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php line 93

    at Doctrine\DBAL\Driver\PDOStatement->execute(null)
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/Statement.php line 168

    at Doctrine\DBAL\Statement->execute()
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php line 281

    at Doctrine\ORM\Persisters\Entity\BasicEntityPersister->executeInserts()
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 1014

    at Doctrine\ORM\UnitOfWork->executeInserts(object(ClassMetadata))
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 378

    at Doctrine\ORM\UnitOfWork->commit(null)
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/EntityManager.php line 356

    at Doctrine\ORM\EntityManager->flush(null)
        in /project_home/var/cache/dev/appDevDebugProjectContainer.php line 7072

    at DoctrineORMEntityManager_00000000751279ee000000007e7efeea3473a0393d6fcd1415b2fc588e376308->flush(null)
        in /project_home/var/cache/dev/jms_diextra/doctrine/EntityManager_59394e2cc7d86.php line 313

    at EntityManager59394e2cc7d86_546a8d27f194334ee012bfe64f629947b07e4919\__CG__\Doctrine\ORM\EntityManager->flush()
        in /project_home/src/AppBundle/Controller/CalendarController.php line 56

    at AppBundle\Controller\CalendarController->createAction(object(Request))
        in  line 

    at ReflectionMethod->invokeArgs(object(CalendarController), array(object(Request)))
        in /project_home/vendor/jms/cg/src/CG/Proxy/MethodInvocation.php line 84

    at CG\Proxy\MethodInvocation->proceed()
        in /project_home/vendor/jms/security-extra-bundle/Security/Authorization/Interception/MethodSecurityInterceptor.php line 133

    at JMS\SecurityExtraBundle\Security\Authorization\Interception\MethodSecurityInterceptor->intercept(object(MethodInvocation))
        in /project_home/vendor/jms/cg/src/CG/Proxy/MethodInvocation.php line 79

    at CG\Proxy\MethodInvocation->proceed()
        in /project_home/var/cache/dev/jms_diextra/proxies/AppBundle-Controller-CalendarController.php line 21

    at EnhancedProxye0ff800f_2852d4e43776e45f00f38751350397dbf530e575\__CG__\AppBundle\Controller\CalendarController->createAction(object(Request))
        in  line 

    at call_user_func_array(array(object(CalendarController), 'createAction'), array(object(Request)))
        in /project_home/var/cache/dev/classes.php line 4228

    at Symfony\Component\HttpKernel\HttpKernel->handleRaw(object(Request), 1)
        in /project_home/var/cache/dev/classes.php line 4183

    at Symfony\Component\HttpKernel\HttpKernel->handle(object(Request), 1, true)
        in /project_home/vendor/symfony/symfony/src/Symfony/Component/HttpKernel/Kernel.php line 168

    at Symfony\Component\HttpKernel\Kernel->handle(object(Request))
        in /project_home/web/app_dev.php line 28

    at require('/project_home/web/app_dev.php')
        in /project_home/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Resources/config/router_dev.php line 40

[3] PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'slug' cannot be null
    at n/a
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php line 91

    at PDOStatement->execute(null)
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php line 91

    at Doctrine\DBAL\Driver\PDOStatement->execute(null)
        in /project_home/vendor/doctrine/dbal/lib/Doctrine/DBAL/Statement.php line 168

    at Doctrine\DBAL\Statement->execute()
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php line 281

    at Doctrine\ORM\Persisters\Entity\BasicEntityPersister->executeInserts()
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 1014

    at Doctrine\ORM\UnitOfWork->executeInserts(object(ClassMetadata))
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 378

    at Doctrine\ORM\UnitOfWork->commit(null)
        in /project_home/vendor/doctrine/orm/lib/Doctrine/ORM/EntityManager.php line 356

    at Doctrine\ORM\EntityManager->flush(null)
        in /project_home/var/cache/dev/appDevDebugProjectContainer.php line 7072

    at DoctrineORMEntityManager_00000000751279ee000000007e7efeea3473a0393d6fcd1415b2fc588e376308->flush(null)
        in /project_home/var/cache/dev/jms_diextra/doctrine/EntityManager_59394e2cc7d86.php line 313

    at EntityManager59394e2cc7d86_546a8d27f194334ee012bfe64f629947b07e4919\__CG__\Doctrine\ORM\EntityManager->flush()
        in /project_home/src/AppBundle/Controller/CalendarController.php line 56

    at AppBundle\Controller\CalendarController->createAction(object(Request))
        in  line 

    at ReflectionMethod->invokeArgs(object(CalendarController), array(object(Request)))
        in /project_home/vendor/jms/cg/src/CG/Proxy/MethodInvocation.php line 84

    at CG\Proxy\MethodInvocation->proceed()
        in /project_home/vendor/jms/security-extra-bundle/Security/Authorization/Interception/MethodSecurityInterceptor.php line 133

    at JMS\SecurityExtraBundle\Security\Authorization\Interception\MethodSecurityInterceptor->intercept(object(MethodInvocation))
        in /project_home/vendor/jms/cg/src/CG/Proxy/MethodInvocation.php line 79

    at CG\Proxy\MethodInvocation->proceed()
        in /project_home/var/cache/dev/jms_diextra/proxies/AppBundle-Controller-CalendarController.php line 21

    at EnhancedProxye0ff800f_2852d4e43776e45f00f38751350397dbf530e575\__CG__\AppBundle\Controller\CalendarController->createAction(object(Request))
        in  line 

    at call_user_func_array(array(object(CalendarController), 'createAction'), array(object(Request)))
        in /project_home/var/cache/dev/classes.php line 4228

    at Symfony\Component\HttpKernel\HttpKernel->handleRaw(object(Request), 1)
        in /project_home/var/cache/dev/classes.php line 4183

    at Symfony\Component\HttpKernel\HttpKernel->handle(object(Request), 1, true)
        in /project_home/vendor/symfony/symfony/src/Symfony/Component/HttpKernel/Kernel.php line 168

    at Symfony\Component\HttpKernel\Kernel->handle(object(Request))
        in /project_home/web/app_dev.php line 28

    at require('/project_home/web/app_dev.php')
        in /project_home/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Resources/config/router_dev.php line 40

The only difference I see is in your xml namespace declaration. You are referencing a url for version 3.x whilst using a versing 2.x. The official documentation uses this schema

http://gediminasm.org/schemas/orm/doctrine-extensions-mappin‌​g

make sure to update your xml mapping accordingly:

<?xml version="1.0" encoding="utf-8"?>
<doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping http://doctrine-project.org/schemas/orm/doctrine-mapping.xsd"
                  xmlns:gedmo="http://gediminasm.org/schemas/orm/doctrine-extensions-mappin‌​g">
    <entity repository-class="AppBundle\Repository\EventRepository" name="AppBundle\Entity\Event">
        <id name="id" type="integer" column="id">
            <generator strategy="AUTO"/>
        </id>
        <field name="startDate" type="datetime" column="startDate"/>
        <field name="endDate" type="datetime" column="endDate"/>
        <field name="title" type="string" column="title" length="255"/>
        <field name="slug" type="string" column="slug" length="255" unique="true">
            <gedmo:slug unique="true" updatable="true" fields="title" separator="-" />
        </field>
        <field name="description" type="text" column="description" nullable="true"/>
        <field name="image" type="string" column="image" length="255" nullable="true"/>
        <field name="followers" type="integer" column="followers" nullable="true"/>
        <field name="city" type="string" column="city" nullable="false" />
        <field name="place" type="string" column="place" nullable="true" />
    </entity>
</doctrine-mapping>