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/**
     * Hook to update the offsets for source partitions before offsets are committed. Source tasks can use this
     * hook to update the offsets for any source partition which isn't part of the offsets about to be committed.
     * If any source partition is dropped, then it has no effect on the offsets committed. However, if the offset
     * is set to a null value for any source partition, a tombstone record would be written to the offsets topic
     * for that source partition.
     * @param offsets the offsets that are about to be committed
     *
     * @return A map consisting of offsets that the task wants to update. The default implementation returns {@code null}
     * which means there would not be any changes to the offsets about to be committed.
     * It is important to note that tasks shouldn't modify the original about to be committed offsets map passed as an argument. 
 */
     public Map<Map<String, Object>, Map<String, Object>> updateOffsets(Map<Map<String, Object>, Map<String, Object>> offsets) {
        return null;
    }

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1. If a source partition is missing in the offsets map, the tasks can add that source partition along with it's offsets that the task thinks it should commit to the offsets in the output map.
2. It is also possible that a task might choose to send a tombstone record as an offset. In such cases, a tombstone record would be written to the offsets topic. A connector can use this mechanism to remove offsets for partitions which it knows won't need to be processed anymore. This logic would be very specific to the connector and is not a supplement to  KIP-875: First-class offsets support in Kafka Connect which allows removal of offsets by Cluster Admins. However, it can be very useful in certain connectors (like File or Object based connectors when a file once processed won't need to be reprocessed and can be safely removed from offsets topic) and hence this feature is being added as part of this KIP.
3. If a source partition which was present in the original to be committed offsets map but not present in the returned map, it won't have any impact on the committed offsets i.e the offsets of the dropped source partition would be committed nonetheless.
4. If a task returns an empty map, the behaviour would would be disabled.

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