public String getGroupingString(String label) {
        PrimitiveObject o = getPrimitiveObject(KEY, label, ObjectUtil.STRING, "String");
        if (o == null) {
            return null;
        }
        return (String) o.getObject();
    }
public String getGroupingString ( String label ) { PrimitiveObject o = getPrimitiveObject ( KEY , label , ObjectUtil . STRING , "String" ) ; if ( o == null ) { return null ; } return ( String ) o . getObject ( ) ; }
Get grouping {@link String} value
@param label target label
@return {@link String} value of the label. If it is not null.