Post dated grant causes GrantNav to fail

[mariongalley]

Describe the bug
A Funder called have added a post-dated grant. The guidance/DQT recommend but do not forbid having post-dated grants. This breaks GrantNav views that include the grant, returning a server error 500.

To Reproduce

The following views return the 500 error:

1. All grants sorted by latest award dates
2. Grants filtered to the funder
3. Grants filtered to the funder via "Explore the data" link on their org page

Expected behavior
It should show the grants as normal not returning an error

Screenshots