Problem: when the indexer hasn't finished some pages show an error

[plexus]

Some slow queries we only do once an hour by a component known as the "indexer", it puts a bunch of lookup maps in an atom.

When the app starts it takes a few minutes before this index map is populated, at that point we should show empty pages or some kind of "sit tight" page, but not a 500 error (NullPointerException) as we do now.

In this code chan-name->id is supposed to be a map, but it can also be nil.

(defn channel-days [db chan-name]
  (let [{:keys [chan-day-cnt chan-name->id]} @!indexes]
    (some->> chan-name
             chan-name->id
             chan-day-cnt
             (sort-by first reverse-compare))))

The solution can be as simple as putting some placeholder maps in !indexes

(defonce !indexes (atom {:chan-name->id {} ,,,}))