bool = playoutiter:IsNull()
True if the iterator is NULL, i.e. invalid. If functions
that allocate iterators fail, they might not throw an error but simply set the
iterator to NULL. You can use this function to check if iterator allocation has
failed in which case the iterator will be NULL.
Also, certain getter functions can return a NULL object in case the object
doesn't exist. You can use this function to check if a getter function returned
a NULL handle.
True if the iterator is NULL, otherwise False