C# - List extension methods in .Net

using System;
using System.Collections.Generic;
using System.Linq;

namespace CollectionExtensions
{
    public static class ListExtension
    {
        public static void AddIfNotExists<T>(this List<T> list, T value)
        {
            CheckListIsNull(list);
            if (!list.Contains(value))
                list.Add(value);
        }

        public static void UpdateValue<T>(this IList<T> list, T value, T newValue)
        {
            CheckListAndValueIsNull(list, value);
            CheckValueIsNull(newValue);
            var index = list.IndexOf(value);
            list[index] = newValue;
        }

        public static void DeleteIfExists<T>(this IList<T> list, T value)
        {
            CheckListAndValueIsNull(list, value);
            if (list.Contains(value))
                list.Remove(value);
        }

        public static bool AreValuesEmpty<T>(this IList<T> list)
        {
            CheckListIsNull(list);
            return list.All(x => x == null);
        }

        private static void CheckListAndValueIsNull<T>(this IList<T> list, T value)
        {
            CheckListIsNull(list);
            CheckValueIsNull(value);
        }

        private static void CheckValueIsNull<T>(T value)
        {
            if (value == null) throw new ArgumentNullException(nameof(value));
        }

        private static void CheckListIsNull<T>(this IList<T> list)
        {
            if (list == null) throw new ArgumentNullException(nameof(list));
        }
    }
}