Taking a break when empty? (2,8)

I believe the answer is:

on vacation

I'm a little stuck... Click here to teach me more about this clue!

'empty?' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's an association between them I don't understand?

'taking a break' is the wordplay.
'taking' becomes 'on' (eg one taking drugs is 'on' drugs).
'a break' becomes 'vacation' (I've seen this before).
'on'+'vacation'='ON VACATION'

'when' acts as a link.

Can you help me to learn more?

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app