Properties that contain arrays may be omitted if they are empty, even if they are loaded. For example:

• release-events is omitted if there are no release events, instead of returning "release-events": []
• tracks is omitted if there are no tracks, instead of returning "tracks": []

This is annoying because it requires handling null or undefined properties, or modeling such properties as being optional in a type system (when, for example, in 99% of cases tracks will be present).