Lack of guile one never has to prove in court (9)
I believe the answer is:
innocence
I believe this is a double definition.
'lack of guile' is the first definition.
(absence of cunning and duplicity)
'one never has to prove in court' is the second definition.
(someone is innocent until proven guilty)
(Other definitions for innocence that I've seen before include "Lack of guilt" , "Freedom from guilt" , "Moral purity" , "Absence of guilt" , "Guilelessness" .)