How can all dharmas have no intrinsic reality logically speaking?
Perhaps you should have a good understanding of Culasunnata Sutta and Mahasunnata Sutta to know the Buddha's understanding of Sunnata.
When you attain Nirodha Samapatthi you do not have the perception and feeling. So when you emerge from Nirodha Samapatthi you know that there is a state of Sunnata.
https://www.accesstoinsight.org/tipitaka/an/an04/an04.024.than.html
https://www.accesstoinsight.org/tipitaka/mn/mn.122.than.html