Weird C-N bond in caffeine

I saw this picture on a teacher's wall and I noticed the C single bonded to the N on the right side. How is it possible that carbon has four bonding sites but is only using one in the picture? Is this stable?


[![structure of caffeine](https://i.stack.imgur.com/CFVPV.jpg)](https://i.stack.imgur.com/CFVPV.jpg)


