Config fails to update with error "SearchQuery not valid"

[lambi21]

App deployed as docker container.

When starting the app or trying to change and save some settings, the error "Error: Settings error: Error: SearchQuery is not valid. Cannot read properties of undefined (reading 'indexOf')" shows up at the top.

More detailed, the log shows:
[ERROR] ErrorDTO {
code: 60,
message: "Settings error: Error: SearchQuery is not valid. Cannot read properties of undefined (reading 'indexOf')",
details: Error: SearchQuery is not valid. Cannot read properties of undefined (reading 'indexOf')
at Object.validateSearchQuery (/app/src/common/SearchQueryUtils.js:140:19)
at ConfigDiagnostics.testAlbumCoverConfig (/app/src/backend/model/diagnostics/ConfigDiagnostics.js:210:45)
at ConfigDiagnostics.testConfig (/app/src/backend/model/diagnostics/ConfigDiagnostics.js:271:33)
at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
at async updateSettings (/app/src/backend/middlewares/admin/SettingsMWs.js:41:13),
request: { method: '', url: '' }

However, in the "Cover" section of the config (UI), no search query is entered. No idea where exactly the error occurs in the config.
When deleting the config.json, the container does not even start up anymore...

[lythandas]

Same here. Deleted the config.json file, started the container and the message reappears.