Hi,
We have a rather interesting thing - in our invoice design we include the City/State/Postal field and if we crate a client manually via the ninja UI and leave the State field empty the invoice generates normally and there is no null value anywhere. However if we send no value for State via API then the invoice contains a ‘null’ where State is supposed to be.
Example:
https://www.dropbox.com/s/pi02rp0k5awhqy2/state.jpg?dl=0