Going to undefined facets causes a 500 error

[dbrower]

Visiting a facet page which doesn't exist causes a 500 error instead of the expected 404 error. For example, visit https://dl.vecnet.org/catalog/facet/xxx

[dbrower]

Some investigation shows this is a blacklight error. Blacklight does not check that @facet is non-nil at this line:

https://github.com/projectblacklight/blacklight/blob/master/lib/blacklight/catalog.rb#L83

[dbrower]

Pin the previous link to a specific version of blacklight (since they keep changing the line numbers)
https://github.com/projectblacklight/blacklight/blob/d9e94b5e5f034e286763d80af8c31b85f27f1699/lib/blacklight/catalog.rb#L83