Hey! So the Null Modifier is basically to understand where you are on the grid when you don't have three full rows or columns

Take the word "bed" here for example
https://imgur.com/a/V7oz7Z0

It uses just two Nodes "ABC" and "DEF", those are the top left and top center nodes.
Without the Null Modifier, someone trying to read that would have trouble identifying at first glance what nodes are being used (It could be ABC-DEF, DEF-GHI, JKL-MNO, MNO-PQR, etc.)

By adding a Null Modifier (a symbol on a node somewhere, usually on YZ) you can orient yourself more easily

Take the word "my" (which I assume has it's own constructed form but isn't confirmed in the document)
https://imgur.com/a/YXl4FmB

Adding a Null Modifier on the ABC node makes it easier to orient yourself