The most common and most likely answer to this crossword clue is the 9 letter word NIHILISTS
I've seen this crossword clue in Financial Times
N
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H
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L
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More clues leading to the result NIHILISTS
- Negative thinkers sit in his complex outside Lima
- Old revolutionaries back at home greeting Rolls
- Is nothing sacred to them?
- Frightfully thin lips – is first layer of paint not needed for such as Warhol and Duchamp?
- Believers in nothing as “nil” – is this unusual?
- Part of UK greeting schedules for extreme sceptics
Buddy explains!

The straight part
We know that "Believers in nothing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case believers in nothing = nihilists.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NIHILISTS mean?
NIHILISTS noun- A person who accepts or champions nihilism.
- An absolute skeptic; a person who believes in the truth of nothing.