System.getProperty("file.encoding.pkg") == null ???

[Amn]

The following code:
*System.getProperty("file.encoding.pkg");*
in my Debian 11 box using Java 17 reports "null", I was expecting 
something like UTF-x.
I did a search on the net in the hope to find some explanation regarding 
the behaviour of the above code, but to no avail. Can anyone help me 
understand the behaviour of the above method call?

Thanks in advance.
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