AsyncTabCompleteEvent shouldn't store Immutable Lists

Spigot-API-Patches/AsyncTabCompleteEvent.patch

@@ -13,7 +13,7 @@ completion, such as offline players.
 
 diff --git a/src/main/java/com/destroystokyo/paper/event/server/AsyncTabCompleteEvent.java b/src/main/java/com/destroystokyo/paper/event/server/AsyncTabCompleteEvent.java
 new file mode 100644
-index 00000000..1e81fe1c
+index 00000000..2fa4cb1c
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/event/server/AsyncTabCompleteEvent.java
 @@ -0,0 +0,0 @@
@@ -42,6 +42,7 @@ index 00000000..1e81fe1c
 +
 +package com.destroystokyo.paper.event.server;
 +
++import com.google.common.collect.ImmutableList;
 +import org.bukkit.Location;
 +import org.bukkit.command.Command;
 +import org.bukkit.command.CommandSender;
@@ -49,6 +50,7 @@ index 00000000..1e81fe1c
 +import org.bukkit.event.Event;
 +import org.bukkit.event.HandlerList;
 +
++import java.util.ArrayList;
 +import java.util.List;
 +
 +/**
@@ -107,6 +109,9 @@ index 00000000..1e81fe1c
 +     * @param completions the new completions
 +     */
 +    public void setCompletions(List<String> completions) {
++        if (completions instanceof ImmutableList) {
++            completions = new ArrayList<>(completions);
++        }
 +        this.completions = completions;
 +    }
 +