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/ParameterDialog.java
private CLabel errorMessageLine;
	
	private Button allowNull, allowBlank, doNotEcho, isHidden, needSort;
	
	private Button importValue, changeDefault, changeFormat, createDataSet;
	
	private Button dynamicRadio, staticRadio;
	
	private Combo dataTypeChooser, controlTypeChooser, defaultValueChooser;
	
	private Combo dataSetChooser, columnChooser, displayTextChooser;
	
	private Label previewLabel;
	private TableViewer valueTable;
	private String lastDataType, lastControlType;
	private String formatCategroy, formatPattern;
	private String defaultValue;
	private Composite valueArea;
	private List columnList;
	private IStructuredContentProvider contentProvider = new IStructuredContentProvider( ) {
		public void dispose( )
		{
		}
		public void inputChanged( Viewer viewer, Object oldInput,
				Object newInput )
		{
		}
		public Object[] getElements( Object inputElement )
		{
			ArrayList list = ( (ArrayList) inputElement );