if a query does not provide the expected number of datapoints, fill in missing points with null

Querying for a weeks worth of data when there is only a day of data will return only a day, and the graph would show only a day. This fix pads out the remaining 6 days of data with `null` so that the graph is representative of the requested date range.
Will this work for "gaps" in the graph, where we monitor something for a while stop and then pick it back up?