Word count practice - need to fix index-out-of-range bug

WordCountPractice.cs

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

class Solution
{
    public static string[,] WordCountEngine(string document)
    {
        if(document == null || document.Length == 0)
        {
          return new string[0,0];
        }
      
        var lowered = document.ToLower(); 
        lowered.Replace('\'','\0'); // you'll -> youll
        
        var splitted = Regex.Split(lowered, "[. !]"); // a.b!c =>"a","b","c"
      
        var dictionary = putToDict(splitted); 
        Console.WriteLine("Debug code is here!  AAAA");
      
        var sorted = applyBucketSort(dictionary); 
      
        // output to dimension array 
        var length = sorted.Length; 
      
        var sortedToArray = new List<string[]>(); 
      
        Console.WriteLine("Debug code is here! BBBB");
      
        for(int i = length - 1; i >= 0; i++)
        {
          var current = sorted[i]; 
          
          if(current != null)
          {
            foreach(var item in current)
            {
              sortedToArray.Add(new string[]{item, i.ToString()}); 
            }
          }
        }
      
        Console.WriteLine("Debug code is here! CCCC");
      
        var dimension = new string[sortedToArray.Count + 1, 2]; 
      
        for(int i = 0; i < sortedToArray.Count; i++)
        {
           dimension[i, 0]  = sortedToArray[i][0];
           dimension[i, 1]  = sortedToArray[i][1]; 
        }      
      
        return dimension; 
    }
  
    private static Dictionary<string, int> putToDict(string[] words)
    {      
       var dict =  new Dictionary<string, int>(); 
      
       foreach(var item in words)
       {
         if(dict.ContainsKey(item))
         {
            dict[item]++;
         }
         else 
           dict.Add(item, 1);
       }
      
      return dict; 
    }

    private static List<string>[] applyBucketSort(Dictionary<string, int>  dict)
    {
      var maxValue = 0; 
      foreach(var pair in dict)
      {
        var value = pair.Value; 
        if(maxValue < value)
        {
          maxValue = value;
        }
      }
      
      var sorted = new List<string>[maxValue + 1]; 
      
      for(int i = 0; i < maxValue + 1; i++)
      {
        sorted[i] = new List<string>(); 
      }
      
      foreach(var pair in dict)
      {
        var key   = pair.Key;
        var value = pair.Value; 
        
        sorted[value].Add(key); 
      }
      
      return sorted; 
    }
  
    static void Main(string[] args)
    {
        var dimension = WordCountEngine("a a b c");  // a 2, b 1, c 1
        var rows = dimension.GetLength(0);
        var cols = dimension.GetLength(1); 
      
        for(int row = 0; row < rows; row++)
        {
          for(int col = 0; col < cols; col++)
          {
            Console.Write(dimension[row, col] + " ");
          }
          Console.WriteLine("new Line"); 
        }
    }
}
/*
upcase -> lower case
' replace ''
split string by delimters ". !" - regular expression 

group words -> how many time Dictionary< string, int> 
Sort them -> order by descending order 

LINQ - nlogN - I am learning 

bucket sort 
value 3, "practice"
value 2, "perfect"
value 1, "by", "get", ...
  
  send to two dimension 
  */