Object property causing error

Question

I have this object property called "Categories" which can be shown here:

private List<Category.Categories> _categories;
        public List<Category.Categories> Categories
        {
            get { return _categories; }
            set
            {
                if (!Enum.IsDefined(typeof(Category.Categories), value))
                {
                    _categories = null;
                }

                _categories = value;
            }
        }

I try to return my object with this property but all I get is a `System.NullReferenceException: Object reference not set to an instance of an object. error. If I remove this property from the instantiaziation return then I have no problems. I'm not sure why this causes an error. The property only wants to accept enums from this class:

    public class Category
    {
        public enum Categories
        {
            Footwear,
            Electronics,
            Jewellery,
            Restaurants,
            Services,
            Apparel
        }
    }

Finally this is how I'm setting the property:

Categories = { Categories.Apparel }

Answer 1

You have to initialize your list to store list form the set property

private List<Category.Categories> _categories = new List<Category.Categories>();