fix null errors, migrate internal API to new methods

src/main/java/com/songoda/ultimatestacker/UltimateStacker.java

@@ -445,15 +445,13 @@ public class UltimateStacker extends SongodaPlugin {
      * @return true if this material will not stack
      */
     public static boolean isMaterialBlacklisted(ItemStack item) {
-        if (ServerVersion.isServerVersionAtLeast(ServerVersion.V1_13)) {
-            return isMaterialBlacklisted(item.getType());
+        CompatibleMaterial mat = CompatibleMaterial.getMaterial(item);
+        if(mat == null) {
+            return true;
+        } else if (mat.usesData()) {
+            return isMaterialBlacklisted(mat.getMaterial(), mat.getData());
         } else {
-            CompatibleMaterial mat = CompatibleMaterial.getMaterial(item);
-            if (mat.usesData()) {
-                return isMaterialBlacklisted(mat.getMaterial(), mat.getData());
-            } else {
-                return isMaterialBlacklisted(mat.getMaterial());
-            }
+            return isMaterialBlacklisted(mat.getMaterial());
         }
     }
 
@@ -461,7 +459,7 @@ public class UltimateStacker extends SongodaPlugin {
      * Check to see if this material is not permitted to stack
      *
      * @param type Material to check
-     * @param data daya value for this item (for 1.12 and older servers)
+     * @param data data value for this item (for 1.12 and older servers)
      * @return true if this material will not stack
      */
     public static boolean isMaterialBlacklisted(Material type, byte data) {

src/main/java/com/songoda/ultimatestacker/listeners/ItemListeners.java

@@ -1,7 +1,6 @@
 package com.songoda.ultimatestacker.listeners;
 
 import com.songoda.core.compatibility.CompatibleSound;
-import com.songoda.core.compatibility.ServerVersion;
 import com.songoda.core.utils.BlockUtils;
 import com.songoda.ultimatestacker.UltimateStacker;
 import com.songoda.ultimatestacker.settings.Settings;
@@ -37,28 +36,27 @@ public class ItemListeners implements Listener {
         event.setCancelled(true);
 
         int specific = instance.getItemFile().getInt("Items." + itemStack.getType().name() + ".Max Stack Size");
-        int max = specific == -1 && new ItemStack(itemStack.getType()).getMaxStackSize() != 1 ? maxItemStackSize : specific;
+        int max;
 
-        if (ServerVersion.isServerVersionAtLeast(ServerVersion.V1_13) && Methods.isMaterialBlacklisted(itemStack.getType()))
-            max = new ItemStack(itemStack.getType()).getMaxStackSize();
-
-        if (!ServerVersion.isServerVersionAtLeast(ServerVersion.V1_13) && Methods.isMaterialBlacklisted(itemStack.getType(), itemStack.getData().getData()))
+        if (UltimateStacker.isMaterialBlacklisted(itemStack))
             max = new ItemStack(itemStack.getType()).getMaxStackSize();
+        else
+            max = specific == -1 && new ItemStack(itemStack.getType()).getMaxStackSize() != 1 ? maxItemStackSize : specific;
 
         if (max == -1) max = 1;
 
-        int newAmount = Methods.getActualItemAmount(event.getEntity())
-                + Methods.getActualItemAmount(item);
+        int newAmount = UltimateStacker.getActualItemAmount(event.getEntity())
+                + UltimateStacker.getActualItemAmount(item);
 
         if (newAmount > max) return;
 
-        Methods.updateItemAmount(item, itemStack, newAmount);
+        UltimateStacker.updateItemAmount(item, itemStack, newAmount);
         event.getEntity().remove();
     }
 
     @EventHandler(priority = EventPriority.HIGH, ignoreCancelled = true)
     public void onInvPickup(InventoryPickupItemEvent event) {
-        if (!Settings.STACK_ITEMS.getBoolean() || !Methods.hasCustomAmount(event.getItem())) return;
+        if (!Settings.STACK_ITEMS.getBoolean() || !UltimateStacker.hasCustomAmount(event.getItem())) return;
         event.setCancelled(true);
 
         Methods.updateInventory(event.getItem(), event.getInventory());
@@ -77,7 +75,7 @@ public class ItemListeners implements Listener {
             return; //Compatibility with Shop instance: https://www.spigotmc.org/resources/shop-a-simple-intuitive-shop-instance.9628/
         }
 
-        Methods.updateItemAmount(event.getEntity(), itemStack, event.getEntity().getItemStack().getAmount());
+        UltimateStacker.updateItemAmount(event.getEntity(), itemStack, event.getEntity().getItemStack().getAmount());
     }
 
     @EventHandler(priority = EventPriority.HIGH, ignoreCancelled = true)

src/main/java/com/songoda/ultimatestacker/utils/Methods.java

@@ -32,7 +32,7 @@ import org.bukkit.util.Vector;
 public class Methods {
 
     public static void updateInventory(Item item, Inventory inventory) {
-        int amount = Methods.getActualItemAmount(item);
+        int amount = UltimateStacker.getActualItemAmount(item);
         ItemStack itemStack = item.getItemStack();
         final int maxStack = itemStack.getMaxStackSize();
 
@@ -51,7 +51,7 @@ public class Methods {
         if (amount <= 0)
             item.remove();
         else
-            Methods.updateItemAmount(item, itemStack, amount);
+            UltimateStacker.updateItemAmount(item, itemStack, amount);
     }
 
     // Do not touch! API for older plugins