for (String funcName : funcNames) {
AggregateFunction func = functions.get(funcName);
if (func == null)
throw new UnsupportedOperationException(String.format("Unsupported aggregate function:\"%s\".",
funcName));
func.merge(accumulator, source, operation);
}
}
public void mergeAll(Aggregation.Builder accumulator, Aggregation source, SliceOperation operation) {