subsonicupdate fails cryptically when server is not available

Problem

Running this command:

$ beet -vv mbsync

Led to this problem:

subsonicupdate: URL is https://[redacted].com/rest/startScan
subsonicupdate: auth type is password
subsonicupdate: Error: Expecting value: line 1 column 1 (char 0)

This happened because my Subsonic server was down, so the issue is just that beets should print a better error message when this happens.

Setup

• OS:
• Python version: 3.13.1
• beets version: 2.2.0
• Turning off plugins made problem go away (yes/no): n/a

My configuration (output of beet config) is:

(paste here)

I'll retry in a few days with a minimal config, I'm assuming mbsync needs a change to happen to actually run subsonicupdate.