Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
multiDataSet.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				refreshValueTable( );
				updateButtons( );
			}
		} );
	}
	private void createDynamicParamsPart( Composite parent )
	{
		Composite comp = new Composite( parent, SWT.NULL );
		comp.setLayout( UIUtil.createGridLayoutWithoutMargin( ) );
		comp.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		Label label = new Label( comp, SWT.NULL );
		label.setText( LABEL_PARAMETERS );
		table = new Table( comp, SWT.FULL_SELECTION
				| SWT.HIDE_SELECTION
				| SWT.BORDER );
		GridData data = new GridData( GridData.FILL_HORIZONTAL );
		data.heightHint = 100;
		table.setLinesVisible( true );
		table.setHeaderVisible( true );
		table.addKeyListener( new KeyAdapter( ) {
			public void keyReleased( KeyEvent e )
			{
				
				if ( e.keyCode == SWT.DEL )
				{
					deleteRow( );
				}