Collector finds it more difficult to keep nothing (7)
I believe the answer is:
hoarder
'collector' is the definition.
(hoarder is a kind of collector)
'more difficult to keep nothing' is the wordplay.
'more difficult' becomes 'harder' ('hard' is associated in meaning with 'difficult').
'to keep' is an insertion indicator.
'nothing' becomes 'o' (O resembles 0).
'harder' placed around 'o' is 'HOARDER'.
'finds it' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for hoarder that I've seen before include "One with hidden store" , "Person gathering and storing objects" , "Saver" , "One saves" , "Person acting like a squirrel" .)