Don't attempt to add NULL keys to a ConcurrentHashMap. Fixes #21

ProtocolLib/src/main/java/com/comphenix/protocol/concurrency/PacketTypeSet.java

@@ -6,6 +6,7 @@ import java.util.Set;
 
 import com.comphenix.protocol.PacketType;
 import com.comphenix.protocol.injector.packet.PacketRegistry;
+import com.google.common.base.Preconditions;
 
 import net.minecraft.util.com.google.common.collect.Maps;
 
@@ -32,18 +33,26 @@ public class PacketTypeSet {
 	 * @param type - the type to add.
 	 */
 	public synchronized void addType(PacketType type) {
-		types.add(type);
+		Class<?> packetClass = getPacketClass(type);
+		types.add(Preconditions.checkNotNull(type, "type cannot be NULL."));
+		
+		if (packetClass != null) {
 			classes.add(getPacketClass(type));
 		}
+	}
 	
 	/**
 	 * Remove a particular type to the set.
 	 * @param type - the type to remove.
 	 */
 	public synchronized void removeType(PacketType type) {
-		types.remove(type);
+		Class<?> packetClass = getPacketClass(type);
+		types.remove(Preconditions.checkNotNull(type, "type cannot be NULL."));
+		
+		if (packetClass != null) {
 			classes.remove(getPacketClass(type));
 		}
+	}
 	
 	/**
 	 * Retrieve the packet class associated with a particular type.