private static void CheckRandomNulls(ListNode node, int count, int nullsPercentage)
        {
            var randomNullsCount = node.Random != null ? 0 : 1;
            var dataNullsCount   = node.Data != null ? 0 : 1;

            var index = 1;

            while (node.Next != null && index < count)
            {
                node = node.Next;
                if (node.Random == null)
                {
                    randomNullsCount++;
                }
                if (node.Data == null)
                {
                    dataNullsCount++;
                }
                index++;
            }

            if (node.Next != null || index != count)
            {
                throw new InvalidDataException();
            }

            var limit = TestsHelper.CalculateLimit(count, nullsPercentage);
            var nulls = count - limit;

            Assert.IsTrue(nulls == randomNullsCount);
            Assert.IsTrue(nulls == dataNullsCount);
        }