I don’t know why you want to use a nullable float for pitch, but I don’t get an error for using one. Are you using the latest NC version 1.5.8?
By the way, a nullable float will not show up for inspection as well as it won’t be serialized. To avoid the GUI error if you do use some older version, you could simply make it private or add [HideInInspector] on top of it if you do want to leave it public for some reason.