Flatten Array on .Net Fiddler version

FlattenArray.cs

using System;
using System.Collections.Generic;
using System.Text;

//see at link: https://dotnetfiddle.net/5HGX96

namespace FlattenArrayExample
{
	public static class Program
	{
		public static void Main()
		{

			//arrange
			#region arrange section
				#region jagged array sample
					int[][] jaggedArray;
					jaggedArray = new int[3][];
					jaggedArray[0] = new int[1];
					jaggedArray[1] = new int[2];
					jaggedArray[2] = new int[3];

					jaggedArray[0][0] = 1;
					jaggedArray[1][0] = 2;
					jaggedArray[1][1] = 3;
					jaggedArray[2][0] = 4;
					jaggedArray[2][1] = 5;
					jaggedArray[2][2] = 6;
				#endregion jagged array sample

				#region nested array sample
					object[][] nestedArray;
					nestedArray = new object[3][];
					nestedArray[0] = new object[1];
					nestedArray[1] = new object[2];
					nestedArray[2] = new object[3];

					nestedArray[0][0] = new object[] { 4,5,6, new object[3] { 6,7,8} };

					nestedArray[1][0] = 2;
					nestedArray[1][1] = 3;
					nestedArray[2][0] = 4;
					nestedArray[2][1] = 5;
					nestedArray[2][2] = 6;
				#endregion nested array sample
					
			#endregion

			//act
			//var flattenedArray = ArrayUtils.GetFlattenedIntArray(jaggedArray);
      var flattenedArray = ArrayUtils.GetFlattenedIntArray(nestedArray);

			//check
			if (flattenedArray != null)
			{
				var flattenedArraySerialized = new StringBuilder();
				foreach (var el in flattenedArray)
				{
					flattenedArraySerialized.Append(string.Format("{0},",el));
				}
				Console.WriteLine(string.Format("flattened array -> [{0}]", flattenedArraySerialized));
			}
			Console.ReadLine();
		}

	}

	public static class ArrayUtils
	{
		public static int[] GetFlattenedIntArray(object jaggedArray)
		{

			var flattenedArray = new List<int>();

			var jaggedArrayType = jaggedArray.GetType();
			var expectedType = typeof(int);

			if (jaggedArrayType.IsArray)
			{
          if (expectedType.IsAssignableFrom(jaggedArrayType.GetElementType()))
          {
						foreach (var el in jaggedArray as int[])
						{
							flattenedArray.Add(el);
						}
					}
					else
					{
						foreach (var el in jaggedArray as object[])
						{
							foreach (var retIntEl in GetFlattenedIntArray(el))
							{
								flattenedArray.Add(retIntEl);
							}
						}
					}
			}
			else if (jaggedArrayType == expectedType)
			{
				flattenedArray.Add((int)jaggedArray);
			}
			else
			{
				return new int[0];
			}
			return flattenedArray.ToArray();
		}
	}

}