Escaping penalty if second bed unoccupied (4-4)

I believe the answer is:

scot-free

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'escaping penalty' is the definition.
I can't tell whether this defines the answer.

'second bed unoccupied' is the wordplay.
'second' becomes 's' (common abbreviation).
'bed' becomes 'cot' (cot is a kind of bed).
'unoccupied' becomes 'free' ('free' can be similar in meaning to 'unoccupied').
's'+'cot'+'free'='SCOT-FREE'

'if' is the link.

Can you help me to learn more?

(Other definitions for scot-free that I've seen before include "Unscathed" , "(Get away) incurring no penalty" , "Unpunished, at liberty like Jock or Angus" , "Completely without penalty" , "See 12" .)

I've seen this clue in The Independent.

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