All Buddhas preach emptiness. Why? Because they wish to crush the concrete ideas of the students. If a student even clings to an idea of emptiness, he betrays all Buddhas.
When your mind doesn't stir inside, the world doesn't arise outside. When the world and the mind are both transparent, this is true vision. And such understanding is true understanding.
To see nothing is to perceive the Way, and to understand nothing is to know the Dharma, because seeing is neither seeing nor not seeing, and because understanding is neither understanding nor not understanding.