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 ScalarParameterHandle selectedParameter;
	
	protected ScalarParameterHandle newParameter = null;
	private String defaultValue;
	private String formatPattern;
	private String formatCategroy;
	private boolean loading = true;
	private Button allowNull;
	private int maxStrLengthProperty;
	private int maxStrLengthOption;
	private String PROPERTY_LABEL_STRING[] = {
			LABEL_PARAM_NAME,
			LABEL_GROUP_PROMPT_TEXT,
			LABEL_PARAMTER_PROMPT_TEXT,
			LABEL_DATA_TYPE,
			LABEL_DISPLAY_TYPE,
			LABEL_DEFAULT_VALUE
	};
	private String OPTION_LABEL_STRING[] = {
			LABEL_HELP_TEXT, LABEL_FORMAT_AS, LABEL_LIST_LIMIT
	};
	protected int getMaxStrLength( String string[], Control control )
	{
		int len = UIUtil.getMaxStringWidth( string, control );
		return len;
	}
	/**
	 * 
	 * Constructor.
	 *