def testNoData(self):
    agg = aggregation.Aggregation({
      'a': {
        '*': [aggregation.Sum()]
      }
    })
    agg.addSource('source1', {'a': {}})
    agg.result()
This used to infinite loop.
dataset/ETHPy150Open Cue/scales/src/greplin/scales/aggregation_test.py/AggregationTest.testNoData