title: GWT Cell Table selection with Checkbox
body: <p>I'm trying to replicate in my project <a href="http://samples.gwtproject.org/samples/Showcase/Showcase.html#!CwCellTable" rel="nofollow noreferrer">this GWT example</a>, but I can't get my code to work correctly, I do not recieve any error but the CheckBox simple do not show up.</p>
  
  <p>this is my code</p>
  
  <pre><code>      public static final ProvidesKey&lt;InventarioByNegDTO&gt; KEY_PROVIDER = new ProvidesKey&lt;InventarioByNegDTO&gt;() {
              @Override
              public Object getKey(InventarioByNegDTO item) {
                  return item == null ? null : item.getKey();
              }
          };
          final SelectionModel&lt;InventarioByNegDTO&gt; selectionModel = new MultiSelectionModel&lt;&gt;(
                  KEY_PROVIDER);
  
  
   ...
     buildTable(){
       negoziTable.addColumn(checkColumn,"Test");
              negoziTable.setColumnWidth(checkColumn, 10d, Style.Unit.PCT);
  
              selectionModel.addSelectionChangeHandler(new SelectionChangeEvent.Handler() {
                  @Override
                  public void onSelectionChange(SelectionChangeEvent selectionChangeEvent) {
                      Window.alert(selectionChangeEvent.toDebugString());
                  }
              });
  
              negoziTable.setSelectionModel(selectionModel,
                      DefaultSelectionEventManager.&lt;InventarioByNegDTO&gt; createCheckboxManager(negoziTable.getColumnIndex(checkColumn)));
  }
  </code></pre>
  
  <p>The <code>buildTable</code> is called <code>@PostCostruct</code>. </p>
  
  <p>Actually if I look into the source code of the generated page the checkbox is in it.</p>
  
  <pre><code>&lt;div style="outline-style:none;" __gwt_cell="cell-gwt-uid-84"&gt;
       &lt;input type="checkbox" tabindex="-1"&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>but is not visible in the page.</p>
  
  <p>Where am I doing wrong?</p>