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