Create Collection of type Class

Im trying to write a function that given a class it will build an object of that type (using reflection). Its working so far but im having trouble with Collections as members.

public static <T> T object(Class<T> type) throws NoSuchMethodException, ClassNotFoundException, InvocationTargetException, InstantiationException, IllegalAccessException {

            T object = getNullInstanceOf(type);

            List<Field> fields = Arrays.asList(object.getClass().getDeclaredFields());

            for (Field f : fields) {
                f.setAccessible(true);
                if (Modifier.isFinal(f.getModifiers())) {
                    continue;
                }
                try {
                    Object fieldValue = f.get(object);
                    if (f.getType().equals(CharSequence.class) || f.getType().equals(String.class)) {
                        f.set(object, f.getName());
                    } else if (f.getType().equals(Integer.TYPE)) {
                        f.set(object, 1);
                    } else if (f.getType().equals(Double.TYPE)) {
                        f.set(object, 2.0);
                    } else if (f.getType().equals(Long.TYPE)) {
                        f.set(object, 3L);
                    } else if (isClassCollection(f.getType())) {
                        f.set(object,
                                ((Collection) getNullInstanceOf(f.getType())) // this throws a "No Such Method Exists" Exception
                                    .add(object(f.getGenericType().getClass()))); 
                    } else if (!(f.getType().equals(type))) {
                        f.set(object, object(f.getType()));
                    } else {
                        return null;
                    }
                } catch (Exception e) {
                    System.err.println("Could not access:" + f.getName());
                    continue;
                }
            }
            return object;
        }

        public static boolean isClassCollection(Class<?> c) {
            return Collection.class.isAssignableFrom(c)
                    || Map.class.isAssignableFrom(c);
        }

        private static <T> T getNullInstanceOf(Class<T> type) throws InvocationTargetException, InstantiationException,
                IllegalAccessException, NoSuchMethodException, ClassNotFoundException {
            Class<?> clazz = Class.forName(type.getName());
            Constructor<?> ctor = clazz.getConstructor();
            return (T) ctor.newInstance();
        }
    }

The issue im having is that when I try to create an instance of the collection, whether it be a set, list, or map, those classes are abstract. Is there a way to just pick a random implementation or do I have to hardcode a concrete subclass for every abstract class?