Date picker breaks newsletter analytics page

[TylerFisher]

When I change the start date of the measured data in the analytics dashboard newsletter analytics page, I receive an application error (means something is returning a 500).

[chelsea-tnc]

Repro steps:

1. Visit the site for an org: https://[YOUR_ORG]/tinycms/analytics/newsletter. Be sure to use an organization that has more traffic to repro the issue reliably.
2. Change the start date for the data range

Expected Result: Data should load according to the date range.

Actual Result: An application error occurs. Screenshot below.

Note: This issue does not come up as often because some orgs prefer to use Google Analytics directly versus TinyCMS' analytics features.