There are built-in merge policies, such as:
com.hazelcast.map.merge.PassThroughMergePolicy: the entry will be added if there is no
existing entry for the key.
com.hazelcast.map.merge.PutIfAbsentMapMergePolicy: the entry will be added if the merging
entry doesn't exist in the cluster.
com.hazelcast.map.merge.HigherHitsMapMergePolicy: the entry with the higher number of hits wins.
com.hazelcast.map.merge.LatestUpdateMapMergePolicy: the entry with the latest update wins.
Default policy is 'com.hazelcast.map.merge.PutIfAbsentMapMergePolicy'