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
nameEditor.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		nameEditor.addModifyListener( new ModifyListener( ) {
			public void modifyText( ModifyEvent e )
			{
				updateMessageLine( );
			}
		} );
		createLabel( propertiesSection, LABEL_PROMPT_TEXT );
		promptTextEditor = new Text( propertiesSection, SWT.BORDER );
		promptTextEditor.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		createLabel( propertiesSection, LABEL_PARAM_DATA_TYPE );
		dataTypeChooser = new Combo( propertiesSection, SWT.READ_ONLY
				| SWT.DROP_DOWN );
		dataTypeChooser.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		dataTypeChooser.setItems( ChoiceSetFactory.getDisplayNamefromChoiceSet( DATA_TYPE_CHOICE_SET ) );
		dataTypeChooser.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				changeDataType( );
				updateCheckBoxArea( );
			}
		} );
		createLabel( propertiesSection, LABEL_DISPALY_TYPE );
		controlTypeChooser = new Combo( propertiesSection, SWT.READ_ONLY
				| SWT.DROP_DOWN );
		controlTypeChooser.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		controlTypeChooser.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				changeControlType( );