Symfony2: Auth using Doctrine2 entity - password set to blank value after saving an entity
security:
    encoders:
        ISELoginBundleEntityUser:
            algorithm: sha1
            iterations: 1
            encode_as_base64: false
    providers:
        main:
            entity:
                class: ISELoginBundleEntityUser
                property: username

class User implements UserInterface {
    // ...
    public function eraseCredentials() {
        $this->password = null;
        $this->salt = null;
    }
    // ...
}

public function createAction() {
    // ...
    if ($form->isValid()) {
        $em = $this->get('doctrine')->getEntityManager();
        $em->persist($product);
        $em->flush();
        return $this->redirect($this->generateUrl('product_create', array('created' => true)));
    }
    // ...
}