of the private method
_compileLanguageLevelsFiles(List<? extends File> files, List<? super CompilerError> errors)
in DefaultCompilerModel has been weakened to
_compileLanguageLevelsFiles(List<? extends File> files, List<CompilerError> errors) {
to avoid tripping over a compiler bug. Since the method is only called from one site, the more general signature (while more elegant) is unnecessary.
