Paper compatibility

src/main/java/xyz/hynse/foliaflow/util/SchedulerUtil.java

@@ -0,0 +1,28 @@
+package xyz.hynse.foliaflow.util;
+
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Entity;
+import org.bukkit.plugin.Plugin;
+
+public class SchedulerUtil {
+
+    private static Boolean IS_FOLIA = null;
+
+    private static boolean tryFolia() {
+        try {
+            Bukkit.getAsyncScheduler();
+            return true;
+        } catch (Throwable ignored) {}
+        return false;
+    }
+
+    private static Boolean isFolia() {
+        if (IS_FOLIA == null) IS_FOLIA = tryFolia();
+        return IS_FOLIA;
+    }
+
+    public static void runLaterEntity(Entity entity, Plugin plugin, Runnable runnable, int ticks) {
+        if (isFolia()) entity.getScheduler().runDelayed(plugin, (task) -> runnable.run(), null, ticks);
+        else Bukkit.getScheduler().runTaskLater(plugin, runnable, ticks);
+    }
+}

src/main/java/xyz/hynse/foliaflow/watcher/PortalWatcher.java

@@ -10,7 +10,9 @@ import org.bukkit.event.EventHandler;
 import org.bukkit.event.Listener;
 import org.bukkit.event.entity.EntityChangeBlockEvent;
 import org.bukkit.util.Vector;
+
 import xyz.hynse.foliaflow.FoliaFlow;
+import xyz.hynse.foliaflow.util.SchedulerUtil;
 
 import static xyz.hynse.foliaflow.util.VelocityUtil.getBlockMovingTo;
 
@@ -35,9 +37,8 @@ public class PortalWatcher implements Listener {
             dummy.setVelocity(dummyVel);
 
             // Add vector seems vanilla.
-            dummy.getScheduler().runDelayed(FoliaFlow.instance,
+            SchedulerUtil.runLaterEntity(dummy, FoliaFlow.instance,
-                task -> dummy.setVelocity(dummyVel.add(new Vector(0, 0.45, 0))),
+                () -> dummy.setVelocity(dummyVel.add(new Vector(0, 0.45, 0))),
-                null,
                 2
             );
         }