title: register a custom json with maps
body: <p>I want to create a json like that : </p>
  
  <p><strong>Expected result:</strong></p>
  
  <pre><code>{
      "id": "1",
      "author": "firas",
      "templatename": "view",
      "typetemp": "factsheet",
      "structure": [
        {
          "nb_columns": 6,
          "title_linechart": "product",
          "xAxis_linechart": "productname",
          "yAxis_linechart": "productcolor"   
        },
        {
         "type": "piechart",
         "percentage" : 81
        },
        {
          ....
        }]
  }
  </code></pre>
  
  <p><strong>The field structure has dynamic fields</strong></p>
  
  <p>This my Entity: </p>
  
  <pre><code>public class Template {
  
  @Id
  private String id;  
  private String author;
  private String templatename;
  private String typetemp;
  private Map &lt;String, Object&gt; structure;
  }
  </code></pre>
  
  <p>Result I had :</p>
  
  <pre><code>{
  "id": "1",
  "author": "firas",
  "templatename": "view",
  "typetemp": "factsheet",
  "structure": {
      "nb_columns": 6,
      "title_linechart": "product",
      "xAxis_linechart": "productname",
      "yAxis_linechart": "productcolor",
      "type": "piechart",
      "percentage" : 81
  }
  </code></pre>
  
  <p>So I changed the type of <code>structure</code> to <code>List&lt;Map&lt;String,Object&gt;&gt;</code> but it gives me this error :</p>
  
  <pre><code>Failed to instantiate java.util.List using constructor NO_CONSTRUCTOR with arguments
  </code></pre>
  
  <p>Can anyone help me ?</p>