Fixed `find_empty_masks` for `CMX` #4719

Job	Run time
macos-latest-py313	1h 9m 36s
ubuntu-latest, ephemeris_connection	1m 7s
ubuntu-latest, black	26s
ubuntu-latest, py313-test-cov	1h 35m 53s
ubuntu-latest, notebooks	5m 29s
ubuntu-latest, oldestdeps	28m 18s
	3h 20m 49s

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