Fixing invalid entity Sylius\Bundle\CoreBundle\Entity\Variant.
The error was :
 The field Sylius\Bundle\CoreBundle\Entity\Variant#images is on the inverse side of a bi-directional relationship, but the specified mappedBy association on the target-entity Sylius\Bundle\CoreBundle\Entity\VariantImage#variant does not contain the required 'inversedBy=images' attribute.