requested changes

src/main/java/ch/njol/skript/aliases/Aliases.java

@@ -557,6 +557,11 @@ public static EntityData<?> getRelatedEntity(ItemData data) {
 	 * <p>Item types provided by this method are updated when aliases are
 	 * reloaded. However, this also means they are tracked by aliases system
 	 * and NOT necessarily garbage-collected.
+	 *
+	 * <p>Relying on this method to create item types is not safe,
+	 * as users can change aliases at any point. ItemTypes should instead be created
+	 * via {@link Material}s, {@link org.bukkit.Tag}s, or any other manual method.
+	 *
 	 * @param name Name of item to search from aliases.
 	 * @return An item.
 	 * @throws IllegalArgumentException When item is not found.

src/main/java/ch/njol/skript/entity/BoatChestData.java

@@ -33,27 +33,8 @@
 
 public class BoatChestData extends EntityData<ChestBoat> {
 
-	private static Material oakBoat = null;
-	private static Material spruceBoat = null;
-	private static Material birchBoat = null;
-	private static Material jungleBoat = null;
-	private static Material acaciaBoat = null;
-	private static Material darkOakBoat = null;
-
 	static {
 		if (Skript.classExists("org.bukkit.entity.ChestBoat")) {
-			//noinspection ConstantConditions
-			oakBoat = Material.getMaterial("OAK_CHEST_BOAT");
-			//noinspection ConstantConditions
-			spruceBoat = Material.getMaterial("SPRUCE_CHEST_BOAT");
-			//noinspection ConstantConditions
-			birchBoat = Material.getMaterial("BIRCH_CHEST_BOAT");
-			//noinspection ConstantConditions
-			jungleBoat = Material.getMaterial("JUNGLE_CHEST_BOAT");
-			//noinspection ConstantConditions
-			acaciaBoat = Material.getMaterial("ACACIA_CHEST_BOAT");
-			//noinspection ConstantConditions
-			darkOakBoat = Material.getMaterial("DARK_OAK_CHEST_BOAT");
 			EntityData.register(BoatChestData.class, "chest boat", ChestBoat.class, 0,
 				"chest boat", "any chest boat", "oak chest boat", "spruce chest boat", "birch chest boat",
 				"jungle chest boat", "acacia chest boat", "dark oak chest boat");
@@ -131,17 +112,17 @@ public boolean isOfItemType(ItemType itemType) {
 
 		ItemStack stack = itemType.getRandom();
 		Material type = stack.getType();
-		if (oakBoat == type)
+		if (type == Material.OAK_CHEST_BOAT)
 			ordinal = 0;
-		else if (spruceBoat == type)
+		else if (type == Material.SPRUCE_CHEST_BOAT)
 			ordinal = TreeSpecies.REDWOOD.ordinal();
-		else if (birchBoat == type)
+		else if (type == Material.BIRCH_CHEST_BOAT)
 			ordinal = TreeSpecies.BIRCH.ordinal();
-		else if (jungleBoat == type)
+		else if (type == Material.JUNGLE_CHEST_BOAT)
 			ordinal = TreeSpecies.JUNGLE.ordinal();
-		else if (acaciaBoat == type)
+		else if (type == Material.ACACIA_CHEST_BOAT)
 			ordinal = TreeSpecies.ACACIA.ordinal();
-		else if (darkOakBoat == type)
+		else if (type == Material.DARK_OAK_CHEST_BOAT)
 			ordinal = TreeSpecies.DARK_OAK.ordinal();
 		return hashCode_i() == ordinal + 2 || (matchedPattern + ordinal == 0) || ordinal == 0;
 	}

src/main/java/ch/njol/skript/expressions/ExprSpawnerType.java

@@ -22,6 +22,7 @@
 import org.bukkit.Material;
 import org.bukkit.block.Block;
 import org.bukkit.block.CreatureSpawner;
+import org.bukkit.entity.EntityType;
 import org.bukkit.event.Event;
 import org.eclipse.jdt.annotation.Nullable;
 
@@ -51,9 +52,12 @@ public class ExprSpawnerType extends SimplePropertyExpression<Block, EntityData>
 	@Override
 	@Nullable
 	public EntityData convert(Block block) {
-		if (block.getType() != Material.SPAWNER)
+		if (!(block.getState() instanceof CreatureSpawner))
 			return null;
-		return EntityUtils.toSkriptEntityData(((CreatureSpawner) block.getState()).getSpawnedType());
+		EntityType type = ((CreatureSpawner) block.getState()).getSpawnedType();
+		if (type == null)
+			return null;
+		return EntityUtils.toSkriptEntityData(type);
 	}
 
 	@Nullable