Recursive function practice - dictionary talk

Recursive_practice_Dictionary.cs

// Flat a ctionary 
// key: string 
// value is string, sometimes it is dictionary 
// value '1' - string
// 'a': '2'    key 'a' value string '2'
// 'c':  key, value is Dictionary 
// key1: 1
// value, how can I determine that it is a string or dictionary 
// Key2.a: '2'
// key2.b: '3'
//  key is constructed by concatenated key2 -> DFS -> recursive function 
// keystring prefix = empty string 
// create new Dictionary <string, string> 
//  step 1: Dictionary -> keys -> iterate on the key
// step 2: for each key, value object -> Determine Runtime type -> string , Dictionary
// step 3: output the key value pair to new dictionary -> key, value is the same
// step 4: if value is Dictinary, continue step 1 -> pass into key string prefix
// return new dictionary <string, string> 
using System;

class LearningExperience {
   static void Main(string[] args) {
      Console.WriteLine("Meet a talent and talk about algorithm");
      var data = new Dictionary<string, object>(); 
      data.Add('key1','1'); 
      data.Add('key2', new Dictionary<..>)
         
      var flatten = new Dictionary<string, string>(); 
      var flattenOnes = FlatternDictionaryRecursive(data, flattern, string.emtpy);
   }
   
   /// key1: 1
   /// DFS -> overflow -> too deep -> iterative solution out-of-stack
   // 
   public static void FlatternDictionaryRecursive(IDictionary<string, object> data, Dictionary<string, object> flattern, string prefix )
   {
      if(data == null || data.Count == 0) return; 
      
      foreach(string key in data.Keys)
      {
         var current = data[key]; 
         var newKey = (prefix == null)? key : (prefix +'.' +key) ; 
         if(current.IsString())
         {
            flattern.Add(newKey, current);
         }
         else
         {
            // it is a dictionary 
            prefix = newKey; // Key2
            FlatternDictionaryRecursive(current, falttern, prefix); 
         }
      }
      
      // do nothing 
      return; 
   }
}