FlatFileStorage saving async throwing Assertion Error exception

[TheLimeGlass]

Skript/Server Version

2.8.0-dev
1.20.1 Paper

Bug Description

Assertion error exception thrown pointing to assert Bukkit.isPrimaryThread()

Expected Behavior

To not throw an assertion exception every save

Steps to Reproduce

I just saved displays into a global variable which is temporary.

spawn a block display at player
set {_hack} to last spawned block display
add {_hack} to {displays::*}

This gets around the parse time warning of stating that an entity cannot be saved to a variable. I don't believe this has anything to do with this issue. Just stating that this is the only thing that can be in ram variables for it to be saving with.

Errors or Screenshots

java.lang.AssertionError: null
        at ch.njol.skript.registrations.Classes.serialize(Classes.java:723) ~[Skript.jar:?]
        at ch.njol.skript.variables.FlatFileStorage.save(FlatFileStorage.java:498) ~[Skript.jar:?]
        at ch.njol.skript.variables.FlatFileStorage.save(FlatFileStorage.java:487) ~[Skript.jar:?]
        at ch.njol.skript.variables.FlatFileStorage.saveVariables(FlatFileStorage.java:436) ~[Skript.jar:?]
        at ch.njol.skript.variables.FlatFileStorage$1.run(FlatFileStorage.java:280) ~[Skript.jar:?]
        at org.bukkit.craftbukkit.v1_20_R1.scheduler.CraftTask.run(CraftTask.java:101) ~[paper-1.20.1.jar:git-Paper-196]
        at org.bukkit.craftbukkit.v1_20_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:57) ~[paper-1.20.1.jar:git-Paper-196]
        at com.destroystokyo.paper.ServerSchedulerReportingWrapper.run(ServerSchedulerReportingWrapper.java:22) ~[paper-1.20.1.jar:?]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) ~[?:?]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) ~[?:?]
        at java.lang.Thread.run(Thread.java:833) ~[?:?]

Other

Databases should always save async, this assertion error should be removed, or should only sync during serialization for collecting the value.

Agreement

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