Add robustness to leading null values in series in 'ewma_by_time'.
#438
| Job | Run time |
|---|---|
| 1m 50s | |
| 3m 15s | |
| 1m 1s | |
| 4m 28s | |
| 1m 56s | |
| 4m 22s | |
| 2m 24s | |
| 14s | |
| 4m 9s | |
| 3m 19s | |
| 2m 30s | |
| 3m 39s | |
| 2m 29s | |
| 0s | |
| 35m 36s |