Fixed `find_empty_masks` for `CMX` #4725

Job	Run time
macos-latest-py313	1h 6m 40s
ubuntu-latest, ephemeris_connection	1m 7s
ubuntu-latest, black	25s
ubuntu-latest, py313-test-cov	1h 33m 42s
ubuntu-latest, notebooks	5m 11s
ubuntu-latest, oldestdeps	28m 6s
	3h 15m 11s

Provide feedback