I just installed spigot-1.15.2.jar from getbukkit.org, started it, opped my player, relogged and it worked fine.
I created a new folder, put the server jar inside, got the BuildTools jar from the spigot wiki, executed the BuildTools just as instructed on the spigot wiki and everything was fine. BUT: as soon as i typed "op M4GG1_" (M4GG1_ is obviously my igname), the console spat out a weird error: https://hastebin.com/ezowopazul.bash (yup, it really is that long). I suspected nothing bad at all, but as soon as I relogged into the sever, the server instantly crashed and my client said: "Internal Exception: java.io.IOException: An existing connection was forcibly closed by the remote host". The server said something like "Exception in server tick loop".

I suspect it being an error related to the ops.json file, because as soon as I delete it, it works until I op my player again.

Why is that and how can I fix it. I just wanted to program some minecraft plugins.

Notes:

• This is not my first time doing spigot related stuff. I'm familiar with the whole download server, execute BuildTools, program plugins thing but this I've never seen.
• I already searched Google but didn't got anything useful.
• I didn't change any server files manually. I, as said, only deleted the ops.json once.
• I tried it with --rev latest and --rev 1.15.2 as arguments on BuildTools

Thanks in advance

The log from the server: https://hastebin.com/suzeyucudu.md
The crash log from the server: https://hastebin.com/jopujefope.cs