title: Linq to Dictionary<string, List<string>> with Null values
body: <p>I do have a list a <code>Culture</code> and a list of Translation:</p>
  
  <pre><code>public class Translation
  {
      public string key { get; set; }
      public string value { get; set; }
      public string cultureId { get; set; }
  }
  </code></pre>
  
  <hr>
  
  <pre><code>public async Task&lt;IActionResult&gt; ReactGetResources(string module = "shared")
  {
      string[] Languages = { "en-US", "fr-FR", "it-IT", "es-ES" };
  
      List&lt;Translation&gt; Translation = new List&lt;Translation&gt;();
      Translation.Add(new Translation { key = "hello", value = "Hello", cultureId = "en-US" });
      Translation.Add(new Translation { key = "hello", value = "Bonjour", cultureId = "fr-FR" });
      Translation.Add(new Translation { key = "hello", value = "Buongiorno", cultureId = "it-IT" });
      Translation.Add(new Translation { key = "goodbye", value = "Good Bye", cultureId = "en-US" });
      Translation.Add(new Translation { key = "goodbye", value = "Au revoir", cultureId = "fr-FR" });
      Translation.Add(new Translation { key = "goodbye", value = "adiós", cultureId = "es-ES" });
  
      Dictionary&lt;string, List&lt;string&gt;&gt; query = Translation
          .OrderBy(o =&gt; o.cultureId)
          .GroupBy(o =&gt; o.key)
          .ToDictionary(g =&gt; g.Key, g =&gt; g.Select(x =&gt; x.value).ToList());
  
      return Json(query);
  }
  </code></pre>
  
  <hr>
  
  <p>The current code <code>IActionResult</code> return:</p>
  
  <pre><code>{
    "hello": [
      "Hello", //en
      "Bonjour", //fr
      "Buongiorno" //it
    ],
    "goodbye": [
      "Good Bye", //en
      "Au revoir", //fr
      "Adiós", //es
    ]
  }
  </code></pre>
  
  <hr>
  
  <p>But i expect to add the <code>Null</code> values for the missing translation:
  <code>{ "en-US", "fr-FR", "it-IT", "es-ES" }</code></p>
  
  <pre><code>{
    "hello": [
      "Hello", //en
      "Bonjour", //en
      "Buongiorno", //it
       null //es
    ],
    "goodbye": [
      "Good Bye", //en
      "Au revoir", //fr
      null, //it
      "Adiós" //es
    ]
  }
  </code></pre>
  
  <p>Can it be done with only <code>Linq</code>? Or maybe i should do a <code>loop</code> in the dictionary et repopulate the vales? </p>