Jar 1.8.8 server

This error is related to a problem sending packets, and occurs due to an unexpected null value that should represent a packet or structure type. The main error appears on the line:

java.lang.NullPointerException: type cannot be null in com.google.common.base.Preconditions.checkNotNull(Preconditions.java:229)

This error points out that some mandatory parameter is null when sending a specific packet (PacketPlayOutSpawnEntity). This typically happens on servers with plugins that use ProtocolLib or similar libraries, where network packets are intercepted or modified before being sent to the client.