Drawing of box with nothing in it (7)
I believe the answer is:
cartoon
'drawing' is the definition.
(type of drawing)
'box with nothing in it' is the wordplay.
'box' becomes 'carton' (carton is a kind of box).
'with nothing' becomes 'o' (I can't explain this - if you can you should give a lot more credence to this answer).
'in it' is an insertion indicator.
'carton' enclosing 'o' is 'CARTOON'.
'of' is the link.
Can you help me to learn more?
(Other definitions for cartoon that I've seen before include "Amusing or satirical drawing" , "eg 'Tom & Jerry'" , "Comic strip" , "Witty drawing" , "Humorous drawing or film of a succession of them" .)