Unmappable characters in filename break project detection

I'm using a Github Codespace with the default image. It has a UTF-8 locale:

$ locale
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

In the project there is a file that is using a UTF-8 character in the filename. Until I remove it, the plugin is unable to detect the project. The log file contains the message

java.nio.file.InvalidPathException: Malformed input or input contains unmappable characters: /home/codespace/my-project/target/test-classes/data-files/Grundfl��chen.dat

To me this looks like the filename is UTF-8 (the character is an ä) but the scanner does not treat it as UTF-8 but rather ASCII.

プロジェクトの検出とスキャナーのパス処理から始め、たとえば ä を含む UTF-8 のファイル名を使って Codespace で問題を再現します。InvalidPathException が発生するまで、ファイル名がどのようにデコードされるかを追跡します。ファイルを削除せずにプロジェクトが正常に検出できれば完了です。