All that you understand of mind or consciousness from out of your own experience is accompanied by a more or less subtle thought of an enduring substance that supports it. Eve if you refer to this as Being, or the thing in itself, it is projected as required to endow the experiencing as identity. This is a flaw in most acceptations of idealism. To consistently apply the latter the experiencing or consciousness or spirit would not res on anything outside of itself. Surely this is what is meant by emptiness, the final correction of the bias towards substance.