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
private static final String LABEL_PARAMETERS = Messages.getString( "CascadingParametersDialog.Label.parameters" ); 
	private static final String LABEL_GROUP_PROPERTIES = Messages.getString( "CascadingParametersDialog.Label.group.properties" ); 
	private static final String LABEL_PARAM_NAME = Messages.getString( "CascadingParametersDialog.Label.param.name" ); 
	private static final String LABEL_LIST_LIMIT = Messages.getString( "CascadingParametersDialog.Label.listLimit" ); 
	private static final String LABEL_DATA_TYPE = Messages.getString( "CascadingParametersDialog.Label.dataType" ); 
	private static final String LABEL_DISPLAY_TYPE = Messages.getString( "CascadingParametersDialog.Label.displayType" ); 
	private static final String LABEL_DEFAULT_VALUE = Messages.getString( "CascadingParametersDialog.Label.defaultValue" ); 
	private static final String LABEL_GROUP_MORE_OPTIONS = Messages.getString( "CascadingParametersDialog.Label.group.moreOptions" ); 
	private static final String LABEL_HELP_TEXT = Messages.getString( "CascadingParametersDialog.Label.helpText" ); 
	private static final String LABEL_FORMAT_AS = Messages.getString( "CascadingParametersDialog.Label.formatAs" ); 
	private static final String LABEL_CHANGE_FORMAT_BUTTON = Messages.getString( "CascadingParametersDialog.Label.button.changeFormat" ); 
	private static final String LABEL_PREVIEW_WITH_FORMAT = Messages.getString( "CascadingParametersDialog.Label.preview" ); 
	private static final String LABEL_CREATE_NEW_PARAMETER = Messages.getString( "CascadingParametersDialog.Label.createNewParam" ); 
	private static final String LABEL_SELECT_DATA_SET = Messages.getString( "CascadingParametersDialog.Label.selectDataSet" ); 
	private static final String LABEL_SELECT_DISPLAY_COLUMN = Messages.getString( "CascadingParametersDialog.Label.selectDisplayColumn" ); 
	private static final String LABEL_SELECT_VALUE_COLUMN = Messages.getString( "CascadingParametersDialog.Label.selectValueColumn" ); 
	private static final String LABEL_NO_COLUMN_AVAILABLE = Messages.getString( "CascadingParametersDialog.Label.NoColumnAvailable" ); 
	private static final String BUTTON_ALLOW_NULL_VALUE = Messages.getString( "CascadingParametersDialog.Button.AllowNull" ); 
	private static final String LABEL_SELECT_DATA_SET_MODE = Messages.getString( "CascadingParametersDialog.Label.SelectDataSetMode" ); 
	private static final String RADIO_SINGLE = Messages.getString( "CascadingParametersDialog.Radio.Single" ); 
	private static final String RADIO_MULTIPLE = Messages.getString( "CascadingParametersDialog.Radio.Mutli" ); 
	private static final String COLUMN_NAME = Messages.getString( "CascadingParametersDialog.Label.column.name" ); 
	private static final String COLUMN_DATA_SET = Messages.getString( "CascadingParametersDialog.Label.column.dataSet" ); 
	private static final String COLUMN_VALUE = Messages.getString( "CascadingParametersDialog.Label.column.value" ); 
	private static final String COLUMN_DISPLAY_TEXT = Messages.getString( "CascadingParametersDialog.Label.column.displayText" ); 
	private static final String PARAM_CONTROL_LIST = DesignChoiceConstants.PARAM_CONTROL_LIST_BOX
			+ "/List";