fs.getAttributeView(...) is supposed to return null if the view is not supported

[overheadhunter]

API such as Files.setPosixFilePermissions(...) relies on getAttributeView(...) to return null in case of the requested view not being supported. However, CryptoFS does always return a view, even though it should not. This leads to later NPEs when an attempt is made to use this view but the corresponding view on the ciphertext node is unavailable.

See cryptomator/cryptomator#2238