SPIGOT-4214: Catch attempts to create BlockData for items

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/block/data/CraftBlockData.java

@@ -417,6 +417,8 @@ public class CraftBlockData implements BlockData {
     }
 
     public static CraftBlockData newData(Material material, String data) {
+        Preconditions.checkArgument(material == null || material.isBlock(), "Cannot get data for not block %s", material);
+
         IBlockData blockData;
         Block block = CraftMagicNumbers.getBlock(material);
 

paper-server/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java

@@ -84,6 +84,7 @@ public final class CraftMagicNumbers implements UnsafeValues {
 
         for (Material material : Material.values()) {
             MinecraftKey key = key(material);
+            // TODO: only register if block/item?
             MATERIAL_ITEM.put(material, Item.REGISTRY.get(key));
             MATERIAL_BLOCK.put(material, Block.REGISTRY.get(key));
         }