The event is not cancelable.

The event does not have a result.

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.

ZenScript
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import crafttweaker.forge.api.event.advancement.AdvancementEvent;

AdvancementEvent extends PlayerEvent. That means all methods available in PlayerEvent are also available in AdvancementEvent

Name	Type	Has Getter	Has Setter
Name advancement	Type Advancement	Has Getter true	Has Setter false