default Aggregation<T> sum() {
      return Matchers.extract((Matcher) this).applyRaw(e -> Expressions.aggregation(AggregationOperators.SUM, Matchers.aggregationType(getClass(), Sum.class, "sum", e), e)).createWith(creator());
    }
Used to provide aggregation template for numeric types (eg. {@link Number}).
@param <MINMAX> type of min/max value(s). Can be optional type.
@param <SUM> type of the sum computation. Can be optional type.
@param <AVG> type of the average computation. Can be optional type.
criteria/common/src/org/immutables/criteria/matcher/Aggregation.java