"500: programmer error" (for one resource only)

[crantila]

As reported by @bacor in CANTUS-Project/api#21:

I've been collecting the full CANTUS database through the API and ran into a 500 server error for the following request.

GET /browse HTTP/1.1
Host: abbot.uwaterloo.ca:8888
X-Cantus-Per-Page: 100
X-Cantus-Page: 4637

I then narrowed it down to one specific resource:

GET /browse HTTP/1.1
Host: abbot.uwaterloo.ca:8888
X-Cantus-Per-Page: 1
X-Cantus-Page: 463662

But note that page number on which I got the error was different on the previous day: then I got the error with X-Cantus-Page: 463685. In any case, the response headers for the above request were

Content-Length: 21
Content-Type: text/html; charset=UTF-8
Date: Fri, 05 Oct 2018 10:18:44 GMT
Server: Abbot/0.7.11
X-Cantus-Version: Cantus/0.3.0

This seems a minor issue, since out of all 482115 promised by the API, it returned this error for one resource only.