Bug 166315 Combo box doesn't allow blank when set string type in parameter editor
Combo box doesn't allow blank when set string type in parameter editor Steps to reproduce: 1.New a parameter, display type is Combo Box 2.Select data type as String Expected result: "Allow blank values" is enable. Actual result: "Allow blank values" is gray and can't be checked.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
this( UIUtil.getDefaultShell( ), title );
	}
	/**
	 * Create a new parameter dialog with given title under the specified shell
	 * 
	 * @param parentShell
	 *            the parent shell of the dialog
	 * @param title
	 *            the title of the dialog
	 */
	public ParameterDialog( Shell parentShell, String title )
	{
		super( parentShell, title );
	}
	protected Control createDialogArea( Composite parent )
	{
		Composite composite = (Composite) super.createDialogArea( parent );
		createPropertiesSection( composite );
		createMoreOptionSection( composite );
		UIUtil.bindHelp( parent, IHelpContextIds.PARAMETER_DIALOG_ID );
		return composite;
	}
	private void createPropertiesSection( Composite composite )
	{
		Group propertiesSection = new Group( composite, SWT.NONE );
		propertiesSection.setText( GROUP_PROPERTIES );
		propertiesSection.setLayout( new GridLayout( 2, false ) );
		propertiesSection.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		createLabel( propertiesSection, LABEL_NAME );
		nameEditor = new Text( propertiesSection, SWT.BORDER );