Steps to reproduce it:

1. Install Jenkins 2.0-beta-2.
2. Restart
3. Upgrade Pipeline from 1.15 to 2.0 (in my case 2.0 was not propagated to my nearest UC mirror so the install wizard installed 1.15. I manually changed it to: http://ftp.icm.edu.pl/packages/jenkins/updates/current/update-center.json which already contains 2.0 packages). Make sure you mark all Pipeline related plugins (the ones that were aggregated by workflow-aggregator before 2.0) in the Upgrade tab (otherwise you will stay in 1.15 and only the aggregator is updated).
4. Create a pipeline with the script generated by the sample "Hello World".
5. Build it.
6. It hangs before starting any step and the CPS VM thread dump is empty.