Shape of zero value? (4)

I believe the answer is:

oval

'shape' is the definition.
(I know that oval is a type of conic)

'of zero value?' is the wordplay.
'of' says the answer is hidden in the clue.
'OVAL' is hidden in the letters of 'zero value'.

(Other definitions for oval that I've seen before include "Test site" , "Stretched circle?" , "34 [CRICKETER] 's domain" , "London cricket-ground" , "London cricket ground" .)

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