Graph widget setup:
1. Select item with numeric data in trends.
2. Aggregation function: Sum
3. Aggregation interval - at least 2h (interval should cover multiple hours, where data is present in each of them)
4. Approximation - avg
5. History data selection - trends (to be sure trends are used)

Result: Graph widget will show average of sum per each hour (that is one trend period).
Expected: Graph should show sum of data per selected aggregation interval.