Switching to Numeric input for the Equals node (and possibly others?) while in the middle of wiring one of its inputs understandably throws NullRef errors. I assume because the input you are in the middle of wiring no longer exists.
1. Make an Equal node
2. Click an input to start dragging (but don't connect it to anything)
3. (while still dragging the wire) Switch to Numeric in the Graph Inspector
4. Graph tab blanks out, console continuously filled with NullReferenceException errors
5. Switch to Play Mode and back to fix.
Customer support service by UserEcho