There are two related issues,
Schema editor doesn't handle non-editable schema editor. (FTP Batch source - https://github.com/cdapio/hydrator-plugins/blob/develop/core-plugins/widgets/FTP-batchsource.json#L59-L76)
Schema editor doesn't "No schema" for output. (Google Analytics Batch source - https://github.com/data-integrations/google-analytics-360/blob/develop/widgets/GoogleAnalyticsBatchSource-batchsource.json#L2121-L2122)
We need to handle these two cases.
Side effects of this bug,
For #1 - User won't be able to see proper message that there is no schema available. (Attached screenshot for reference)
For #2 - Users will be able to edit the schema but when they re-open the plugin properties modal they will again see the default schema.