在实体回调中添加Symfony Assert

Question

如何在实体回调中添加Symfony Assert（Notblank（）; Number（）; Email（）; ...）？

示例AppBundle\Entity\TrainingLead：

/**
 * @Assert\Callback
 */
public function rejectedValidate(ExecutionContextInterface $context)
{
    if (null !== $this->rejectedAt) {
        // How to add "Assert\NotBlank()" in rejectedContent" ?
        $context->buildViolation('training_lead.reason')
            ->atPath('rejectedContent')
            ->addViolation()
        ;
    }
}