This regression was introduced in https://github.com/cdapio/hydrator-plugins/commit/016f0e7782a5cfa0d0ccd1d49988e549a628bb9d. You must specify an empty JSON string for filesystem properties in order for the plugin to work.
Once the bug is fixed, there should be unit test associated with validation for all the properties for this source. The unit tests should include both happy path and multiple error path with almost full code coverage for validation
Is this a regression in 6.3.0 too?
Yes for 6.3 its a regression
Can someone change fix version to 6.3.1 too so I can pick it up in a report?