Checking if CAgnTodo has a StartDate

Hi,
I'm copying a ToDo item and pasting it.
I want to check if it has a Start Date and Due Date.

So first I check
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CAgnTodo* iAgnTask;

if (iAgnTask->IsDated())
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If the item is dated, I want to check if it has a Start Date or only a due date.
So I'm doing:

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if (iAgnTask->InstanceStartDate()) ...
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But that cannot be put inside an if.  I have to evaluate to something.
I was trying to find out how to do "!=NULL" or some kind of TTime::Null
But I couldn't find any.

I'm checking if
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if (iAgnTask->InstanceStartDate()!=iAgnTask->DueDate())
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I don't know if that how I'm supposed to do it.
But I think that tells me that there IS a start date.

So can anyone tell me how you can check if a CAgnToDo has a start date or not?
And also, I want to set the Start date of a ToDo item.
How do I do that?

Thanks!