diff --git a/ProtocolLib/src/com/comphenix/protocol/events/PacketContainer.java b/ProtocolLib/src/com/comphenix/protocol/events/PacketContainer.java
index 49bcea17..9b6f3d1b 100644
--- a/ProtocolLib/src/com/comphenix/protocol/events/PacketContainer.java
+++ b/ProtocolLib/src/com/comphenix/protocol/events/PacketContainer.java
@@ -1,5 +1,6 @@
 package com.comphenix.protocol.events;
 
+import org.bukkit.WorldType;
 import org.bukkit.craftbukkit.inventory.CraftItemStack;
 import org.bukkit.inventory.ItemStack;
 
@@ -22,6 +23,17 @@ public class PacketContainer {
 	// Current structure modifier
 	protected StructureModifier<Object> structureModifier;
 	
+	// Check whether or not certain classes exists
+	private static boolean hasWorldType = false;
+	
+	static {
+		try {
+			Class.forName("net.minecraft.server.WorldType");
+			hasWorldType = true;
+		} catch (ClassNotFoundException e) {
+		}
+	}
+	
 	/**
 	 * Creates a packet container for a new packet.
 	 * @param id - ID of the packet to create.
@@ -70,10 +82,22 @@ public class PacketContainer {
 		return structureModifier;
 	}
 	
-	public <T> StructureModifier<T> getPrimitiveModifier(Class<T> primitiveType) {
+	/**
+	 * Retrieves a read/write structure for every field with the given type.
+	 * @param primitiveType - the type to find.
+	 * @return A modifier for this specific type.
+	 */
+	public <T> StructureModifier<T> getSpecificModifier(Class<T> primitiveType) {
 		return structureModifier.withType(primitiveType);
 	}
 	
+	/**
+	 * Retrieves a read/write structure for ItemStack.
+	 * <p>
+	 * This modifier will automatically marshall between the Bukkit ItemStack and the
+	 * internal Minecraft ItemStack.
+	 * @return A modifier for ItemStack fields.
+	 */
 	public StructureModifier<ItemStack> getItemModifier() {
 		// Convert from and to the Bukkit wrapper
 		return structureModifier.<ItemStack>withType(net.minecraft.server.ItemStack.class, new EquivalentConverter<ItemStack>() {
@@ -88,6 +112,13 @@ public class PacketContainer {
 		});
 	}
 	
+	/**
+	 * Retrieves a read/write structure for arrays of ItemStacks.
+	 * <p>
+	 * This modifier will automatically marshall between the Bukkit ItemStack and the
+	 * internal Minecraft ItemStack.
+	 * @return A modifier for ItemStack array fields.
+	 */
 	public StructureModifier<ItemStack[]> getItemArrayModifier() {
 		// Convert to and from the Bukkit wrapper
 		return structureModifier.<ItemStack[]>withType(net.minecraft.server.ItemStack[].class, new EquivalentConverter<ItemStack[]>() {
@@ -115,6 +146,35 @@ public class PacketContainer {
 		});
 	}
 	
+	/**
+	 * Retrieves a read/write structure for the world type enum.
+	 * <p>
+	 * This modifier will automatically marshall between the Bukkit world type and the
+	 * internal Minecraft world type.
+	 * @return A modifier for world type fields.
+	 */
+	public StructureModifier<WorldType> getWorldTypeModifier() {
+	
+		if (!hasWorldType) {
+			// We couldn't find the Minecraft equivalent
+			return structureModifier.withType(null);
+		}
+		
+		// Convert to and from the Bukkit wrapper
+		return structureModifier.<WorldType>withType(net.minecraft.server.WorldType.class, new EquivalentConverter<WorldType>() {
+			@Override
+			public Object getGeneric(WorldType specific) {
+				return net.minecraft.server.WorldType.getType(specific.getName());
+			}
+			
+			@Override
+			public WorldType getSpecific(Object generic) {
+				net.minecraft.server.WorldType type = (net.minecraft.server.WorldType) generic;
+				return WorldType.getByName(type.name());
+			}
+		});
+	}
+	
 	/**
 	 * Retrieves the ID of this packet.
 	 * @return Packet ID.
diff --git a/ProtocolLib/src/com/comphenix/protocol/reflect/StructureModifier.java b/ProtocolLib/src/com/comphenix/protocol/reflect/StructureModifier.java
index e7d76219..39d1b0ce 100644
--- a/ProtocolLib/src/com/comphenix/protocol/reflect/StructureModifier.java
+++ b/ProtocolLib/src/com/comphenix/protocol/reflect/StructureModifier.java
@@ -186,7 +186,7 @@ public class StructureModifier<TField> {
 		
 		StructureModifier<T> result = subtypeCache.get(fieldType);
 		
-		if (fieldType.equals(this.fieldType)) {
+		if (this.fieldType.equals(fieldType)) {
 			
 			// We're dealing with the exact field type.
 			return withConverter(converter);
@@ -196,7 +196,7 @@ public class StructureModifier<TField> {
 			Set<Field> defaults = new HashSet<Field>();
 			
 			for (Field field : data) {
-				if (fieldType.isAssignableFrom(field.getType())) {
+				if (fieldType != null && fieldType.isAssignableFrom(field.getType())) {
 					filtered.add(field);
 					
 					if (defaultFields.contains(field))
@@ -208,7 +208,9 @@ public class StructureModifier<TField> {
 			result = new StructureModifier<T>();
 			result.initialize(targetType, fieldType, filtered, defaults, 
 							  converter, new HashMap<Class, StructureModifier>());
-			subtypeCache.put(fieldType, result);
+			
+			if (fieldType != null)
+				subtypeCache.put(fieldType, result);
 		}
 		
 		// Add the target too