Null data indicates a Signal has no defined value. This is not the same as value of zero. In a TestCase, null data is represented by square gray dots:
Null data dots before a transition
Numeric response Signals have null data between power on and their first transition. It is also possible for a numeric response Signal to change from a defined value to null data after a system reset. See System Reset.
In this example, Value2, a numeric message-based Signal, has null data at power on (time 0). Each time its parent message (MsgHazard) is received, a value is assigned. An MxV Module Reset is asserted at 10 seconds, which resets Value2 to null data. When MsgHazard is received again, a value is assigned again.
Editing Message Fields (message-based signals)
Viewing Signals—No Defined Value (null data)