SysExtension porperyValueMap null

Hi, 

Im trying a simple excercise with SysExtension. I use the base enum WeekDays and i get the error "object not initialized." I debug and i find out that "porpertyValueMap" return a null value. But i dont know why. I have this code:

CLASS VSSClassDayAttribute--------------------------------------------------------------------------------------------

class VSSClassDayAttribute extends SysAttribute
{
WeekDays days;
}

//////////////////////////

public WeekDays parmWeekDays(WeekDays _days = days)
{
days = _days;

return days;
}

////////////////////////

public void new(WeekDays _days)
{
super();

this.parmWeekDays(_days);
}

CLASS VSSClassDayBase----------------------------------------------------------------------------------------------------------

class VSSClassDayBase
{
}

////////////////////////////

protected void new()
{
}

////////////////////////////

public void run()
{
info("@SYS32707");
}

//////////////////////////

public static VSSClassDayBase construct(WeekDays _days)
{
VSSClassDayAttribute atribute = new VSSClassDayAttribute(_days);
VSSClassDayBase base;

base = SysExtensionAppClassFactory::getClassFromSysAttribute(classStr(VSSClassDayBase), atribute);

return base;
}

CLASS CHILD --------------------------------------------------------------------------------------------------------------------------------

[VSSClassDayAttribute(WeekDays::Monday)]
class VSSClassLunes extends VSSClassDayBase
{
}

/////////////////////////////////////////////////////

public void run()
{
super();
info("@SYS5217");
}

I think it is correct, i dont know where is the error. Any suggestions?

Thanks.