Meaning of niggling

(adj) (informal) small and of little importance; "a fiddling sum of money"; "a footling gesture"; "our worries are lilliputian compared with those of countries that are at war"; "a little (or small) matter"; "a dispute over niggling details"; "limited to petty enterprises"; "piffling efforts"; "giving a police officer a free meal may be against the law, but it seems to be a picayune infraction"