Spy traditional beer? Never a mild (6)

I believe the answer is:

gentle

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'a mild' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for gentle that I've seen before include "Not violent, tender" , "Tender - maggot" , "'Do not go . . . . . . into that good night' (Dylan Thomas)" , "Mild, kind, tender" , "'Mild, soft, tender (6)'" .)

I've seen this clue in The Times.

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