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
if ( formatBuilder.open( ) == OK )
		{
			formatCategroy = ( (String[]) formatBuilder.getResult( ) )[0];
			formatPattern = ( (String[]) formatBuilder.getResult( ) )[1];
			updateFormatField( );
		}
	}
	private void updateFormatField( )
	{
		String displayFormat;
		IChoiceSet choiceSet = getFormatChoiceSet( getSelectedDataType( ) );
		if ( choiceSet == null )
		{
			displayFormat = DEUtil.getMetaDataDictionary( )
					.getChoiceSet( DesignChoiceConstants.CHOICE_STRING_FORMAT_TYPE )
					.findChoice( DesignChoiceConstants.STRING_FORMAT_TYPE_UNFORMATTED )
					.getDisplayName( );
		}
		else
		{
			displayFormat = choiceSet.findChoice( formatCategroy )
					.getDisplayName( );
			if ( formatCategroy != DesignChoiceConstants.STRING_FORMAT_TYPE_CUSTOM )
			{
				displayFormat += ":  " + formatPattern; 
			}
		}
		formatField.setText( "" + displayFormat ); 
		changeFormat.setEnabled( choiceSet != null );
		if ( selectedParameter != null )