Bug 153523 OK button in parameter dialog is enabled without default value in combo-box
Description: OK button in parameter dialog is enabled without default value in combo-box Steps to reproduce: 1. New a report parameter, combo-box. 2. Click New button, input abc as value, click OK 3. Set abc as default value and close Edit Parameter dialog. 4. New a data source and dataset 5. Edit the parameter, remove abc value and import values from dataset Expected result: OK button is disabled for there is no default value. Actual result: OK button is enabled.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
* @param parentShell
	 * @param title
	 */
	public CascadingParametersDialog( Shell parentShell, String title )
	{
		super( parentShell, title );
	}
	/**
	 * Constructor.
	 * 
	 * @param title
	 */
	public CascadingParametersDialog( String title )
	{
		super( title );
	}
	protected Control createDialogArea( Composite parent )
	{
		Composite composite = (Composite) super.createDialogArea( parent );
		UIUtil.bindHelp( parent, IHelpContextIds.CASCADING_PARAMETER_DIALOG_ID );
		GridData data = new GridData( );
		data.widthHint = 600;
		maxStrLengthProperty = getMaxStrLength( PROPERTY_LABEL_STRING,
				composite );
		maxStrLengthOption = getMaxStrLength( OPTION_LABEL_STRING, composite );
		composite.setLayoutData( data );
		createGeneralPart( composite );
		createChoicePart( composite );
		createDynamicParamsPart( composite );
		createPropertiesPart( composite );