"If you only read the books that everyone else is reading, you can only think what everyone else is thinking."
The second condition applies:
"If the number of Enemy AP counters is ≥ the number of Cubes in the Raided Cubes Box, move all Enemy AP counters (if any) from the Raided Cubes Box to the Enemy APs Available Box. Reset Cubes. Place the “Defend” counter on the topmost empty space of the Inactive Column of the Enemy Instruction Display and continue to Step 2 of Enemy Operations Segment."
0 AP counters is equal to 0 cubes. Note that the parenthesis confirms what you've seen and that there might not be an AP counters.