Filtering commits by "::something" can cause 500er errors (BB-8876)

When I try to filter the commits showing all commits up to a a bookmark ("::myBookmark"), or if I search for a non-existing bookmark ("::nonExisitingBookmark") the server responds with a 500 error.

How to reproduce:
Assume that "myBookmark" is a bookmark in your repo.
Filtering for "::myBookmark" will cause the problem.