Handle null data

The new dataset is a subset of the original. I thought this meant less rows, but it actually nulls out the values for streets. The data changed and the code wasn't prepared.

This won't fix all failing tests from #56 as the basic problem is those tests are using invalid data. Pull request for that will follow shortly.
This tells me this isn't really a models test. It's testing that CreateSchedules() can handle null street sweeping data. I think CreateSchedules should be a task with this test.