Fun fact: "Δεν υπάρχει" in everyday usage and mostly between younger people is also used for something that's very impressive. Somewhat as a shortcut to "I can't believe this exists".
So Maria might say "Έχεις δεί τι κάνει ο καλλιτέχνης;" ("Have you seen what the artist is doing?") and Panos would answer "Ναι, δεν υπάρχει!" ("Yes, (he) doesn't exist!")
This is talking about something in general, like there were ties in this store last week but now "there is none". Or do you have ties? No, "there is none". I realize that this is a better literal translation of the Greek, but in English when we are talking about something in general we would use the plural and say, "There are none."