@Override
    public String toString() {
        return "" +
                "countMapSize=" + countMap.size() +
                ", valueMapSize=" + valueMap.size() +
                ", age=" + getAge().toString();
    }
Adds entries from another aggregate map into this one.

@param aggregateMap
stroom-statistics/stroom-statistics-impl-sql/src/main/java/stroom/statistics/impl/sql/SQLStatisticAggregateMap.java