@Nonnull
	public static NavigableSet<String> getSystemClassSet() {
		if (classSet == null) {
			synchronized (ClasspathUtil.class) {
				if (classSet == null) {
					classSet = new TreeSet<>();
					ModuleFinder.ofSystem().findAll().stream()
							.map(Unchecked.function(ModuleReference::open))
							.flatMap(Unchecked.function(ModuleReader::list))
							.filter(s -> s.endsWith(".class") && s.indexOf('-') == -1)
							.map(s -> s.substring(0, s.length() - 6))
							.forEach(s -> classSet.add(s));
				}
			}
		}
		return classSet;
	}
@return Set of all system classes.
recaf-core/src/main/java/software/coley/recaf/util/ClasspathUtil.java