public FilterExpression getExpression() {
   final FilterExpression expression = new FilterExpression();
   expression.setOperator(Operator.AND);
   for (final AssertionComposite assertionComposite : this.assertionComposites) {
     expression.getFilterSet().add(assertionComposite.getExpression());
   }
   return expression;
 }
 public void removeAssertion(final AssertionComposite assertion) {
   this.assertionComposites.remove(assertion);
   assertion.dispose();
   refreshGUI();
   if (this.assertionComposites.size() == 0) {
     this.tabItem.setText(Messages.a_condition);
   }
 }