Flatten dictionary - C# code - pramp question - check links inside source code in the following

FlattenDictionary.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FlattenDictionary
{
    class Program
    {
        /*
         * #Flatten a Dictionary

        Given a dictionary, write a function to flatten it. Consider the following 
        input/output scenario for better understanding:

        Input:

        { 'Key1': '1', 'Key2': { 'a' : '2', 'b' : '3', 'c' : { 'd' : '3', 'e' : '1' } } } 
        
        Output:
         
        { 'Key1': '1', 'Key2.a': '2', 'Key2.b' : '3', 'Key2.c.d' : '3', 'Key2.c.e' : '1' }
         */
        static void Main(string[] args)
        {
            var test = new Program();

            var dict = new Dictionary<string, object>();
            dict.Add("Key1", "1");

            //var dict3 = new Dictionary<string, string>();
            // Dictionary<string, object> is not same as Dictionary<string, string>

            var dict3 = new Dictionary<string, object>();
            dict3.Add("d", "3");
            dict3.Add("e", "1");

            var dict2 = new Dictionary<string, object>();
            dict2.Add("a", "2");
            dict2.Add("b", "3");
            dict2.Add("c", dict3);

            dict.Add("Key2", dict2);

            var result = test.FlattenDictionary(dict);

            var dict4 = new Dictionary<string, object>();
            dict4.Add("a","4"); 
            result = test.FlattenDictionary(dict4);
        }

        /// <summary>
        /// Code review on July 18, 2023
        /// http://juliachencoding.blogspot.com/search?q=Flatten+dictionary
        /// https://gist.github.com/jianminchen/74ca7d779505a3f079c667960f773fc7
        /// 
        /// </summary>
        /// <param name="dict"></param>
        /// <returns></returns>
        public Dictionary<string, string> FlattenDictionary(Dictionary<string, object> dict)
        {
            if (dict == null || dict.Count == 0)
            {
                return new Dictionary<string, string>();
            }

            var flatten = new Dictionary<string, string>();

            foreach (var pair in dict)
            {
                var key = pair.Key;
                var valueObject = pair.Value;

                if (valueObject.GetType() == typeof(Dictionary<string, object>))
                {
                    var subDict = FlattenDictionary((Dictionary<string, object>)valueObject);

                    foreach (var childPair in subDict)
                    {
                        var childKey = childPair.Key;
                        var childValue = childPair.Value;

                        var keyComposed = key;
                        var newKey = key.Length == 0 ? "" : keyComposed;
                        var newSubKey = childKey;
                        if (key.Length > 0)
                        {
                            newSubKey = keyComposed + "." + childKey; // bug
                        }

                        newKey = childKey.Length == 0 ? keyComposed : newSubKey;

                        flatten.Add(newKey, childValue);
                    }
                }
                else
                {
                    flatten.Add(key, (string)valueObject);
                }
            }

            return flatten;
        }
    }
}