code: protected String onGetObject(final IModel<T> rowModel)
  	{
  		final IModel<?> propertyModel = DateColumn.this.getDataModel(rowModel);
  		final Date value = (Date)propertyModel.getObject();
  		if (value == null) {
  			return "";
  		}
  		final SimpleDateFormat format = new SimpleDateFormat(dateFormat);
  		return format.format(value);
  	}
docs: Callback method for provide specific behavior on method
  {@link AbstractReadOnlyModel#getObject()}.
  
  @param rowModel
  the row model
  @return the string