deep copy using reflection java

I can't get a container from the class field using reflection. I tried the method below, but got an exception:

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(AbstractList.java:148)
    at java.util.AbstractList.add(AbstractList.java:108)
    at java.util.Collections.addAll(Collections.java:5455)

public static void copy(Object from, Object to) throws NoSuchFieldException, IllegalAccessException {
        Class<?> fromClass = from.getClass();
        Class<?> toClass = to.getClass();
        Field[] sourceFields = fromClass.getDeclaredFields();
        for (Field fromField : sourceFields) {
            Field toField = toClass.getDeclaredField(fromField.getName());
            toField.setAccessible(true);
            fromField.setAccessible(true);
            if (fromField.getType().equals(toField.getType())) {
                if (!(fromField.getType() == String.class || fromField.getType().isPrimitive())) {
                        if (fromField.getType().isAssignableFrom(List.class)) {
                            List list = (List) fromField.get(from);
                            List list1 = (List) toField.get(to);
                            Collections.addAll(list1,list);
                            toField.set(to, fromField.get(from));
                        } else if (fromField.getType().isAssignableFrom(Set.class)) {
                            Set set = (Set) fromField.get(from);
                            Set set1 = (Set) toField.get(to);
                            set1.clear();
                            set.addAll(set1);
                            toField.set(to, fromField.get(from));
                        }
                } else {
                    toField.set(to, fromField.get(from));
                }
            }
        }
    }

I don't want to use methods of copying via serialization, I'm interested in reflection.