Can't load an old jar

[FranklinS12]

Compiled jar with java 8: OSRS Gamepack

Tried with other older jars and similar errors occur. Unsure of the issue, used jdk 17 and 21 for running. Also added java 8's rt lib as a library and continue to get issues

Error:
Exception in thread "main" java.lang.IllegalStateException: Cannot add java/lang/Object.clone()Ljava/lang/Object; as a parent of org/bouncycastle/math/ec/LongArray.clone()Ljava/lang/Object; because it is already a parent at dev.skidfuscator.ir.method.impl.ResolvedAbstractFunctionNode.addParent(ResolvedAbstractFunctionNode.java:100) at dev.skidfuscator.ir.klass.impl.ResolvedKlassNode.inheritFunction(ResolvedKlassNode.java:287) at dev.skidfuscator.ir.klass.impl.ResolvedKlassNode.resolveInternal(ResolvedKlassNode.java:195) at dev.skidfuscator.ir.hierarchy.impl.SkidHierarchy.resolveClasses(SkidHierarchy.java:179)

Loading code:

public static void main(String[] args) throws IOException {

		String inputJar = "231-gamepack" + ".jar";
		
		final Set<ClassNode> classes = loadClasses(new File(inputJar));
		
		final SkidHierarchy skid = new SkidHierarchy();
		skid.resolveClasses(classes);
		
	}
	
	private static Set<ClassNode> loadClasses(File file) throws IOException {
		
		JarFile jarFile = new JarFile(file);
		
		Enumeration<JarEntry> entries = jarFile.entries();
		
		Set<ClassNode> classes = new HashSet<>();
		
		while (entries.hasMoreElements()) {
			
			JarEntry entry = entries.nextElement();
			
			if (!entry.getName().endsWith(".class"))
				continue;
			
			try (InputStream in = jarFile.getInputStream(entry)) {
				
				classes.add(ClassHelper.create(in));
			}
			
		}
		
		jarFile.close();
		return classes;
	}