fix[protocol]: null point

protocol/src/main/java/com/zfoo/protocol/buffer/ByteBufUtils.java

@@ -430,12 +430,6 @@ public abstract class ByteBufUtils {
 
     //-----------------------------------------------------------------------
     //---------------------------------以下方法会被字节码生成的代码调用--------------------------------------
-    public static boolean writePacketFlag(ByteBuf byteBuf, Object packet) {
-        boolean flag = packet == null;
-        byteBuf.writeBoolean(!flag);
-        return flag;
-    }
-
     public static void writePacketCollection(ByteBuf byteBuf, Collection<?> collection, IProtocolRegistration protocolRegistration) {
         if (collection == null) {
             byteBuf.writeByte(0);

protocol/src/main/java/com/zfoo/protocol/registration/EnhanceUtils.java

@@ -183,6 +183,7 @@ public abstract class EnhanceUtils {
 
         var builder = new StringBuilder();
         builder.append("{");
+        builder.append("if ($2 == null) { $1.writeByte(0); return; }");
         builder.append(StringUtils.format("{} packet = ({})$2;", packetClazz.getName(), packetClazz.getName()));
         if (registration.isCompatible()) {
             builder.append("int beforeWriteIndex = $1.writerIndex();");

protocol/src/main/java/com/zfoo/protocol/registration/ProtocolRegistration.java

@@ -74,7 +74,7 @@ public class ProtocolRegistration implements IProtocolRegistration {
     public void write(ByteBuf byteBuf, Object packet) {
         if (packet == null) {
             // equals with ByteBufUtils.writeInt(byteBuf, 0);
-            ByteBufUtils.writeByte(byteBuf, (byte) 0);
+            byteBuf.writeByte(0);
             return;
         }