"У мене немає друга."
Translation:I do not have a friend.
Idiomatic translation of "I don't have any friends" needs adding, and the same for some similar sentences.
Rule of thumb: if it's something that most people have, and in the plural at that (friends, relatives, legs, etc), then "I don't have any..." is the more usual phrasing in English. If it's a singular thing that it's more reasonable that the person doesn't have (a car, a son, a phone, etc), and many people who do have them have only one, then "I don't have a..." is the more natural rendering in those contexts.
The given answer for this one, the closer-to-literal translation of "I don't have a friend" is perfectly correct, but less natural English. "I don't have any friends" is much more natural.
As we're talking about zero friends in each example, as is made clear from the context, this isn't a number error, and should be added to the database.
(Yes, I reported. Just noting here for posterity / momentum)
I may add that plural would also be more natural for Ukrainian: "в мене немає друзів" would sound much more natural. "в мене немає друга" may be a valid (but not a mandatory) choice just with some specific contexts or situations where exactly one friend was mentioned beforehand.