After a long, frustrating day of fruitless troubleshooting of nonexistent software issues on my iPhone, I am beyond frustrated with Apple. (It's the hardware, guys, it's the hardware. Again.)
So when I had to reset all of my iphone's settings and redo the text forwarding and I got THIS stupid "null" thing on my iPad mini, I had pretty much had it. Ready to just sit down and cry. And then go get an Android. 🙂
I AM happy to tell you, though annabel, that turning my iPad mini off and powering it back on fixed it. I tried again and got a normal, numerical code that I could work with.
It is the easiest fix I have had with Apple all day. So try turning your iPad off and then back on. Hope that works for you.