low version upgrade bug

[huanglongchao]

upgrade 6.1.6 -> lastest version, data follower sync from leader, NullPointException

DiffSyncDigest request from null error for slot null,61
java.lang.NullPointerException: null
at com.alipay.sofa.registry.common.model.PublisherUtils.getDatumSummary(PublisherUtils.java:59)

A data follower node has failed to synchronize with the primary node, impacting the high availability of data during the release period. Nonetheless, this issue does not affect business functionality in the short term