以下 c# 代码只是试图找出给定字符串的长度和反转有什么问题

我只是想找出字符串的反面和长度。以下是代码的片段：

    Console.WriteLine("Please Enter your String: ");
        string InputString = Console.ReadLine();
        char[] String_Array = InputString.ToCharArray();
        int Length = 0;
        foreach (char c in String_Array)
        {
            Length++;
        }
        char[] String_Reverse = null;
        for (int i = Length - 1, j = 0; Length >= 0; Length--, j++)
        {
            //Here is the error I am facing, Null Reference Exception
            String_Reverse[j] = String_Array[i];
        }
        string Reverse = new string(String_Reverse);
        Console.WriteLine("Length of the String " + InputString + " is :" + Length + " and Reverse of the String is :" + Reverse);
        Console.ReadLine();