I was having this issue even with beta 15.
What fixed it for me was after uninstalling docker finding for any file or folder named docker and delete the ones that were not part of my projects. After I restarted and installed docker (this time he asked again for my beta key which it didn’t on previous uninstall and install attempts, I guess one of the files/folders I deleted had that data saved) and it started without the null reference error.
However I was still having network issues not being able to pull as described in Docker pull won’t work. I couldn’t make it work using the suggestions present on the thread (they did work for me when I had beta 11 though) but after following the 3 steps on https://beta.docker.com/docs/windows/troubleshoot/#networking-issues and restarting I got it working.
Hope this also helps anyone having similar issues.
P.S. - In the middle of all this, trying to resolve the null reference error I also re-installed Hyper-V but I don’t think it helped. Something to keep in mind though…