arkenfox-cleanup.js: "Source map error" shown in console

[Marc05]

The following error is shown in the console after running arkenfox-cleanup.js:

Source map error: Error: URL constructor:  is not a valid URL.
Stack in the worker:resolveSourceMapURL@resource://devtools/client/shared/source-map-loader/utils/fetchSourceMap.js:56:22
getOriginalURLs@resource://devtools/client/shared/source-map-loader/source-map.js:74:24
workerHandler/</<@resource://devtools/client/shared/worker-utils.js:115:52
workerHandler/<@resource://devtools/client/shared/worker-utils.js:113:13

Resource URL: null
Source Map URL: null
https://firefox-source-docs.mozilla.org/devtools-user/debugger/source_map_errors/?utm_source=mozilla&utm_medium=firefox-console-errors&utm_campaign=default

I'm reporting it since I didn't see anything about this when searching the issue history.