Bundle.type does not have nullflavor in the valueset and code dataType does not support use of the dataAbsentReason extension.

Existing Wording:

In situations where information on a particular data element is missing and the Sender knows the precise reason for the absence of data, the Sender SHALL provide the reason for the missing information using values (such as nullFlavors) from the value set where they exist or using the dataAbsentReason extension.