title: Nest converts first letter of field to lowercase in query
body: <p>I am trying to upsert a dictionary&lt;string, string&gt; to elasticsearch but the first letter of the keys converts to small letter.
  <a href="https://i.stack.imgur.com/NHO7E.png" rel="nofollow noreferrer">the dictionary property in the entity</a></p>
  <pre><code>public Dictionary&lt;string, Dictionary&lt;string, string&gt;&gt; CurrentJson { get; set; }
  public string CURRENT_JSON
  {
      set
      {
          CurrentJson = new Dictionary&lt;string, Dictionary&lt;string, string&gt;&gt;
          { { TableName.ToUpper(), JsonConvert.DeserializeObject&lt;Dictionary&lt;string, string&gt;&gt;(value) } };
      }
  }
  </code></pre>
  <p>the keys when I set the dictionary will be cap. letters</p>
  <p><a href="https://i.stack.imgur.com/7IOzo.png" rel="nofollow noreferrer">upsert function</a></p>
  <pre><code>public async Task&lt;T&gt; Upsert(T document, string username = &quot;N/A&quot;)
  {
      // check if name is duplicated
      if (!await IsUniqueDocument(document))
          throw new Exception(&quot;name duplicated&quot;);
      
      PrepareDocument(document, username);
      
      IndexRequest&lt;T&gt; request = new IndexRequest&lt;T&gt;(document, IndexName, TypeName, document.Id);
      var response = await Client.IndexAsync&lt;T&gt;(request);
      if (response.IsValid) return document;
      // TODO: check thrown error
      throw new Exception(response.Result.ToString());
  }
  </code></pre>
  <p>note: prepareDocument function do not change the dictionary</p>