decodedStringOrNull

Decodes the base64-encoded value to a UTF-8 string, or returns null if not valid UTF-8.

This is the safe version of decodedString that handles binary data gracefully. Use this when the data entry might contain binary (non-text) data.

Null is returned both for a value that is not valid base64 and for bytes that are not valid UTF-8, so this accessor never raises and is safe to call from toString.