CODETOOLS-7903091 updated jtreg to use `Path` instead of `File`. This resulted in some JDK tests failing on Windows, because `InvalidPathException` was thrown. (JDK-8281507)

It would be better to check the validity of the class name more explicitly. These days, `SourceVersion.isName` would be an excellent way to check the name.
https://docs.oracle.com/en/java/javase/11/docs/api/java.compiler/javax/lang/model/SourceVersion.html#isName(java.lang.CharSequence,javax.lang.model.SourceVersion)