Log when it's likely the indexedcodec is gonna fail, because of LAN server derps likely. Try and give some context for debuggers.

src/main/java/net/minecraftforge/fml/common/network/FMLIndexedMessageToMessageCodec.java

@@ -70,6 +70,10 @@ public abstract class FMLIndexedMessageToMessageCodec<A> extends MessageToMessag
     {
         testMessageValidity(msg);
         ByteBuf payload = msg.payload().copy();
+        if (payload.readableBytes() < 1)
+        {
+            FMLLog.log(Level.ERROR, "The FMLIndexedCodec has received an empty buffer on channel %s, likely a result of a LAN server issue. Pipeline parts : %s", ctx.channel().attr(NetworkRegistry.FML_CHANNEL), ctx.pipeline().toString());
+        }
         byte discriminator = payload.readByte();
         Class<? extends A> clazz = discriminators.get(discriminator);
         if(clazz == null)