Fixed a bug that lies within the Spigot API where setting an item in an inventory where the item is a Firework Rocket with power but no effect results in a NullPointer exception because the effects list is null.
This would typically occur when loading graves from the files when the server is starting.

This is solved by adding and subsequently removing a regular effect to initialize the effects list when the firework has no effects.

Should you encounter a message at the server start along the lines of
" Could not load item [Number] for grave [UUID]: ... ItemStack was: ...", there will be an item missing in the grave. In that case, please report that to me so I can manually implement a fix. This issue is not caused by the plugin.