[SOLVED] [1.15.2] Invalid message?

Hey, I'm implementing SimpleImpl atm and when I tried to send a message, I got the error 

"Caused by: java.lang.IllegalArgumentException: Invalid message"

Can somebody tell me what's wrong? 

public class SimpleMessage {
	public String message;

	public SimpleMessage(String message) {
		this.message = message;
	}

	public SimpleMessage() {
	}

	public static SimpleMessage read(PacketBuffer buf) {
		return new SimpleMessage(buf.readString());
	}

	public static void write(SimpleMessage message, PacketBuffer buf) {
		buf.writeString(message.message);
	}

	public static class Handler {
		public static void handle(SimpleMessage message, Supplier<NetworkEvent.Context> context) {
			((NetworkEvent.Context) context.get()).setPacketHandled(true);
			System.out.println(message.message);
		}
	}
}

This is the message class itself

And this is the method I'm using to send it

	public <MSG> void sendToServer(MSG message) {
		channel.sendToServer(message);
	}

Thanks in advance

Edited October 23, 20204 yr by RobinCirex