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 final ITableAreaModifier tableAreaModifier = new ITableAreaModifier( ) {
		public boolean editItem( final Object element )
		{
			final SelectionChoice choice = (SelectionChoice) element;
			boolean isDefault = isDefaultChoice( choice );
			SelectionChoiceDialog dialog = new SelectionChoiceDialog( Messages.getString("ParameterDialog.SelectionDialog.Edit") ); 
			dialog.setInput( choice );
			dialog.setValidator( new SelectionChoiceDialog.ISelectionChoiceValidator( ) {
				public String validate( String displayLabel, String value )
				{
					return validateChoice( choice, displayLabel, value );
				}
			} );
			if ( dialog.open( ) == Dialog.OK )
			{
				choice.setValue( convertToStandardFormat( choice.getValue( ) ) );
				if ( isDefault )
				{
					defaultValue = choice.getValue( );
				}
				return true;
			}
			return false;
		}
		public boolean newItem( )
		{
			SelectionChoice choice = StructureFactory.createSelectionChoice( );