Support nullable field #1237

Job	Run time
test-backup-restore-after-upgrade (docker-compose, standalone, standalone, v2.3.12, master-latest)	40s
test-backup-restore-cross-version (docker-compose, standalone, standalone, 2.2.0-latest, master-l...	43s
test-backup-restore-cli (docker-compose, standalone, standalone)	51s
test-backup-restore-after-upgrade (docker-compose, standalone, standalone, v2.3.12, 2.3-latest)	44s
test-backup-restore-cross-version (docker-compose, standalone, standalone, 2.2.0-latest, 2.4-latest)	50s
test-backup-restore-cli (docker-compose, standalone, cluster)	40s
test-backup-restore-after-upgrade (docker-compose, standalone, standalone, 2.3-latest, master-lat...	43s
test-backup-restore-cross-version (docker-compose, standalone, standalone, 2.3-latest, master-lat...	47s
test-backup-restore-cli (docker-compose, cluster, standalone)	57s
test-backup-restore-after-upgrade (docker-compose, standalone, standalone, 2.3-latest, 2.3-latest)	48s
test-backup-restore-cross-version (docker-compose, standalone, standalone, 2.3-latest, 2.4-latest)	50s
test-backup-restore-cli (docker-compose, cluster, cluster)	43s
test-backup-restore-with-custom-config (helm, standalone, milvus-backup)	1m 54s
test-backup-restore-with-custom-config (helm, standalone, milvus-bucket)	1m 54s
test-backup-restore-with-custom-config (helm, standalone, file, milvus-backup)	1m 51s
test-backup-restore-with-custom-config (helm, standalone, file, milvus-bucket)	1m 55s
test-backup-restore-api	0s
	16m 50s

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