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.

Start with project detection and scanner path handling, reproducing the issue in a Codespace using a UTF-8 filename such as one containing ä. Trace how the filename is decoded until the InvalidPathException occurs; done means the project is detected successfully without removing the file.