The quality of 'emptiness' or of 'non-emptiness' of an object has no direct bearing on the efficacy of the procedure implied by the use of those terms, for it is only the inexistence of the object itself as such that is being indicated: the object can neither be 'empty' nor 'non-empty' nor anything else, for it is not there to be anything or to have any quality. To state that the object is empty, void, or whatever word may be chosen, is begging the question - for then the object is still there to be that, to have that quality or the lack of that quality.
This understanding is a step towards the further understanding that the apparent object is to be located at its source, and not in its manifested appearance.
The Indian analogy of the clay and the pot, and the Chinese analogy of the gold and the lion-image, created by the potter and the goldsmith from the clay and the gold respectively, are imperfect also and really rather misleading, for they too carry on the old and futile attempt to represent by objective images and concepts THIS whose total character is non-character, whose sole being is non-being, whose only objective existence lies in the absolute absence of objectivity and of non-objectivity.
The sole aim of the statement, as of the analogies, is to throw the mind back, to turn it away from objectifying, and return it to its true centre, which is precisely the ultimate non-objectivity from which objectivity springs.
Concurrently this destruction of the concept of the object as a thing-in-itself, or as an objective reality, operates psychologically to the same end in that, by annihilating the object as such, the subject of that object - the immediate subject which reveals it conceptually - is automatically annihilated also. This is inevitable because phenomenal subject and phenomenal object are inseparable, two aspects of a single functioning, and can never be apart at any moment or in any circumstances.
So that when this understanding is applied to all objects, to all phenomena whatever, subject is thereby always eliminated, and it is the elimination of the subjective illusion that matters rather than that of its objective counterpart. The subjective illusion, based on separate individuality, an ego or will-body, operating by supposed volition, can never be annihilated directly - for that would be by means of itself. This, the negative way, is the only possible means of eliminating the pseudo-subject of pseudo-objects, which is the sole factor obstructing our knowledge of this which alone we are, which prevents our 'being' it - though we are it, which prevents our 'living' it throughout our phenomenal manifestation.
There is every reason to suppose and to believe that the moment this understanding becomes spontaneous (that is, the moment we are able directly and unconsciously, entirely non-volitionally, to perceive in this manner - which is direct perception antecedent to name-and-form, prior to temporal interpretation by the objectivisation-process of 'spinning' subject-object) we shall be free of our apparent bondage - for our apparent bondage is just that. This spontaneous direct perception is precisely what the Masters meant when they spoke of the One True Thought, the Thought of the Absolute, or, in the words of the great Shen Hui (668-760), the successor of Hui Neng: 'Silent identification with non-being is the same as that which is described as sudden enlightenment. So also what is described as 'when a single thought is in accord (with the truth) at once you have the ultimate wisdom of the Buddha'.' ('Wisdom', here as elsewhere, i.e. Prajna, means 'Subjectivity' or Non-objective understanding, as Han Shan told us). This is the 'single thought' in question, and that is the reason why the elimination of the objective reality of objects is stressed as the essential method of understanding.
Note: Referring to the enlightenment of the Abbot Ming by Hui Neng the Sixth Patriarch, Fung Yu-lan says: 'The force of the Patriarch's question was to eliminate subject and object. When a man as a subject and its object are eliminated then he is one with 'non-being', and is described as having silent identification with non-being; and by that is meant that not merely the man knows there is non-being but that he is actually identified with non-being.' (The Spirit of Chinese Philosophy, trans. E.R. Hughes, Kegan Paul 1947, p. 166. Also his History of Chinese Philosophy, trans. Derk Bodde, Princeton University Press 1952, Vol. II, p. 397. The former, a slight volume, is perhaps more readily accessible.)