Bug 166315 Combo box doesn't allow blank when set string type in parameter editor
Combo box doesn't allow blank when set string type in parameter editor Steps to reproduce: 1.New a parameter, display type is Combo Box 2.Select data type as String Expected result: "Allow blank values" is enable. Actual result: "Allow blank values" is gray and can't be checked.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
if ( canBeNull( ) && string == null )
		{
			return LABEL_NULL;
		}
		if ( StringUtil.isBlank( string ) || formatCategroy == null )
		{
			return string;
		}
		try
		{
			String pattern = formatPattern;
			if ( formatPattern == null )
			{
				if ( isCustom( ) )
				{
					return string;
				}
				pattern = formatCategroy;
			}
			if ( DesignChoiceConstants.PARAM_TYPE_DATETIME.equals( getSelectedDataType( ) ) )
			{
				Date date = DataTypeUtil.toDate( string, ULocale.US );
				DateFormatter formatter = new DateFormatter( pattern );
				string = formatter.format( date );
			}
			else if ( DesignChoiceConstants.PARAM_TYPE_FLOAT.equals( getSelectedDataType( ) ) )
			{
				string = new NumberFormatter( pattern ).format( DataTypeUtil.toDouble( string )
						.doubleValue( ) );
			}