Steps to Reproduce:

1. Enter The End
2. Build a tower out of a block that the Ender Dragon cannot break at x:0, z:0 (Above the middle of the bedrock perch)
3. Wait until the dragon enters the takeoff phase

Crash Report:

crash-2017-05-10_20.52.06-server.txt

I'm finding it near impossible to recover from this w/o the use of external programs, so if you wish to try it, I don't recommend doing it on an important world that you aren't willing to loose!