Melon has zero information (4)
I believe the answer is:
ogen
'melon' is the definition.
(I've seen this before)
'zero information' is the wordplay.
'zero' becomes 'O' (O resembles 0).
'information' becomes 'gen' (gen can informally mean information).
'o'+'gen'='OGEN'
'has' acts as a link.
(Other definitions for ogen that I've seen before include "Gone (anag.)" , "fruit?" , "Small melon variety" , "Type of melon" .)