java.lang.NullPointerException: Exception in server tick loop

What the log looks like

java\.lang\.NullPointerException: Exception in server tick loop

How to fix it

1. Open the crash report and read the first 1-5 `at ...` lines directly below `java.lang.NullPointerException: Exception in server tick loop`—the Java package names on those lines (for example `blusunrize.immersiveengineering` or `thaumicenergistics`) identify the exact mod(s) that crashed.
2. If those top lines mention `postInit`, `serverStarted`, `Registry`, or `Recipe`, update the top-listed mod and any second mod right beneath it to matching releases for your Minecraft version, ensuring the server and all clients run the exact same `.jar` versions.
3. If a startup crash persists and two mods appear together at the top of the stack trace, open their files in the `config/` folder and disable the cross-mod integration option between them.
4. If the stack trace goes through `Chunk`, `AnvilChunkLoader`, or `TileEntity` classes, a placed block in the world is crashing as its chunk loads: back up your world folder, then test starting the server without chunkloading mods or hybrid server cores such as SpongeForge.
5. If a broken modded block entity still prevents the world from loading after you make a backup, temporarily enable `removeErroringTileEntities` (or `removeErroringBlockEntities` in `forge-server.toml` / `neoforge-server.toml`), start the server once to delete the broken block, and set the option back to `false`.

Check your own log