What is your goal? If you want every second evenly space empty, then just double the Evenly Distance.
However, if you need sequence or compose, the Empty/Null segment will terminate Sequence/Compose. Adding some value to X fixed size should activate Null so Sequence will continue (that can be some very small value like 0.001cm).
Sometimes I use a trick to simulate Null: Add a simple geometry as a box instead of Null but set the Transform Scale X/Y/Z to 0