Nit-picker (7)
(Other definitions for pedant that I've seen before include "Picky type" , "Unimaginative person who insists on petty rules" , "One excessively concerned with minor detail" , "Fussy schoolmaster, academic" , "Panted (anag.)" .)
(Other definitions for fusspot that I've seen before include "Pernickety person" , "One who gets worked up" , "One who worries too much" , "Old woman" , "Perfectionist" .)
'nit-picker' is the definition.
(I've seen this before)
This is all the clue.
(Another definition for niggler that I've seen is " Nit-picker".)