I don't know why this would be null, but thats what the error says..

src/main/java/me/libraryaddict/disguise/utilities/packets/packetlisteners/PacketListenerViewSelfDisguise.java

@@ -40,7 +40,8 @@ public class PacketListenerViewSelfDisguise extends PacketAdapter {
         try {
             final Player observer = event.getPlayer();
 
-            if (observer.getName().contains("UNKNOWN[")) {// If the player is temporary
+            if (observer == null || observer.getName() == null ||
+                    observer.getName().contains("UNKNOWN[")) {// If the player is temporary
                 return;
             }