public String getTaskNames() {
    return getMessageValue(TASK_NAMES_KEY);
  }
SetTaskPartitionMapping is the data format for persisting the partition to task assignments
of a samza job to the coordinator stream.
@param source      the source of the message.
@param partition   the system stream partition serialized as a string.
@param taskNames    the taskNames mapped to the system stream partition.
samza-core/src/main/java/org/apache/samza/coordinator/stream/messages/SetTaskPartitionMapping.java