Possible Clues:

• Empty or unoccupied
• Empty container placed inside another
• Empty tin placed in barrel
• Unoccupied — unthinking
• Ready for occupation
• Holiday worker lacking occupation
• Following five, there's nothing in a thing with nothing in it
• 'For oft, when on my couch I lie / in ... or in pensive mood' (Wordsworth)
• Empty tin in tank
• Container inside another holding nothing