nonexistence vs nullity

nonexistence and nullity both are nouns.

Word	Noun	Adjective	Verb	Adverb
nonexistence	Yes	No	No	No
nullity	Yes	No	No	No

As nouns, nullity is a hyponym of nonexistence; that is, nullity is a word with a more specific, narrower meaning than nonexistence:

Other hyponyms of nonexistence include irreality, unreality, nihility, nothingness, void, impossibility, impossibleness.

nonexistence (noun)	nullity (noun)
the state of not existing	something that is null (especially an enactment that has no legal validity)
	the state of nonexistence