[Druid] Explore view throws error when group by is applied

[vylc]

Chart: Line/Time series
Datasource: Druid

Unsure what is going on--cryptic error is thrown when I try visualizing the dataset as a line chart with a group by on a single dimension. Works fine on the non-Druid datasource

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• I have checked the superset logs for python stacktraces and included it here as text if any
• I have reproduced the issue with at least the latest released version of superset
• I have checked the issue tracker for the same issue and I haven't found one similar

Superset version

Expected results

Actual results

Steps to reproduce

[mistercrunch]

Should be fixed in master