Fixed `find_empty_masks` for `CMX` #4724

Job	Run time
macos-latest-py313	53m 4s
ubuntu-latest, ephemeris_connection	1m 19s
ubuntu-latest, black	27s
ubuntu-latest, py313-test-cov	1h 33m 28s
ubuntu-latest, notebooks	5m 26s
ubuntu-latest, oldestdeps	28m 21s
	3h 2m 5s

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