Why is there no rule for error "Invalid character encountered"

When running sonar-scanner I get this error reported to the terminal -> "
*WARN: Invalid character encountered *
in file com_joomlaupdate/restore.php
at line 6840
*for encoding UTF-8. *
Please fix file content or configure the encoding to be used using property ‘sonar.sourceEncoding’.
"

Checking the file and errors within (duplications etc) are recorded but the invalid character on line 6840 is not one of them (and there are many more repetitions of the same character)

Surely if processing is taken to recognise the situation and output a tailored message in the standard output warning - it should also have a rule (I looked but did not find) and a marker on the code screen pointing out the error condition so that someone could be assigned to fix it.