Falling into DictSetItem()

Hello Radaee.
I use:
long ref = annot.GetRef();
Obj obj = new Obj(ref);
Obj nameOb = obj.DictGetItem("T");

I want to save and read some values using the methods DictSetItem() / DictGetItem(), but it crashes DictGetItem(), what could be the reason?

dear user:
you shall do codes like: you can only get reference of annotation/page/document object.
and Document.Advance_GetObj()
is the only method to get object data.

Thanks for the answer.
But this method requires a premium license, and I only have a professional one. Then tell me why, having a professional license, the annot.GetModifyDate () method does not work for me.
I use:
boolean isSave = annotation.SetModifyDate(CommonUtil.getCurrentDate()); -> (isSave = false)
and
String date = annot.GetModifyDate(); -> (date = null)

dear user:
we checked this method, SetModifyDate() will return false in these condition:
1. annotation is locked.(Annotation.IsLocked() => true)
2. string value is null
3. at least, you need a professional license.
we checked on Android version, and it works.