title: vaadin, getting null pointer when trying to add item to sqlContainer
body: <p>I'm very new to vaadin ( and to java). </p>
  
  <p>i have an table that has an SQLcontainer like so : </p>
  
  <pre><code>public class ProjectTable extends Table {
        public ProjectTable(final DocumentmanagerApplication app) {
            setSizeFull();
            setContainerDataSource(app.getDbHelp().getProjectContainer());
            setImmediate(true);
  
            commit();
            setSelectable(true);
  
        }
      }
  </code></pre>
  
  <p>i have a button and a TextField , to fill data in the table </p>
  
  <pre><code>public void buttonClick(ClickEvent event)
      {
          SQLContainer cont = h.getAssetContainer();
          String dataResult = tf.getValue().toString(); // TEXT FIELD 
          System.out.println(dataResult);
  
  
  
  
  
  
          Object itemId = cont.addItem(); // cont is the container
          **cont.getContainerProperty(itemId , "id").setValue(dataResult);      // BUG IS HERE !!! **  
  
  
  try {
              cont.commit();
          } catch (UnsupportedOperationException e) {
              // TODO Auto-generated catch block
              e.printStackTrace();
          } catch (SQLException e) {
              // TODO Auto-generated catch block
              e.printStackTrace();
          }
  </code></pre>
  
  <p>i keep getting a " null pointer exception" no matter what i do. on the line **cont.getContainerProperty(itemId , "id").setValue(dataResult);</p>
  
  <p>am i doing anything wrong ? and what is null pointer ? </p>
  
  <p>please inform me if anything was unclear.</p>
  
  <p>please help , thanks in advance. </p>