When I try to start the server it shuts itself down

I'm trying to turn on my server but it keeps shutting itself down. Version 1.14.4 Software Spigot / Bukkit. Here is the Crash Report:https://mclo.gs/muOB2Ua

I was able to enter after disabling command blocks. What's the problem? What command is preventing me from starting it? I'm building a KitPvP server. Of course I need to use commands. Which command should not be used?