Flat via Police Department representation? (5)

I believe the answer is:

vapid

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'flat' is the definition.
(I know that flat can be written as vapid)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for vapid that I've seen before include "Boring, flat" , "Insipid, empty" , "Dull, insipid, flat" , "Insipid or uninteresting" , "Offering no stimulation" .)

I've seen this clue in the Sydney Morning Herald.

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