Exception of mapping of ID generation strategy

Hi all,

After updating today Doctrine 2 from master branch I'm getting:

Entity of type "Entity" is missing an assigned ID. The identifier generation strategy for this entity requires the ID field to be populated before EntityManager#persist() is called. If you want automatically generated identifiers instead you need to adjust the metadata mapping accordingly.

Was there a change on the mapping of ID generation strategy? I was using a commit of the master branch from 1 o 2 weeks ago and it was working ok. I took a look at the repo for changes on the last days but I couldn't find anything related to this.

I paste the mapping and entities here:

Element:

/**
 * @ORM\MappedSuperclass
 */
abstract class Element
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="IDENTITY")
     */
    protected $id;
}

File:

/**
 * @ORM\Entity
 * @ORM\Table(name="file")
 * @ORM\InheritanceType("JOINED")
 * @ORM\DiscriminatorColumn(name="discriminator", type="string")
 * @ORM\DiscriminatorMap({
        "image"  = "Image",
    })
 */
abstract class File extends Element
{
     // Fields
}

And Image:

/**
 * @ORM\Entity
 * @ORM\Table(name="image")
 */
class Image extends File
{
     // Fields
}

Thanks in advance!