packer.writePayload(msg) results in NullPointerException

Is this a bug or intended behavior?

import org.msgpack.core.MessageBufferPacker;
import org.msgpack.core.MessagePack;

import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        final MessageBufferPacker packer = new MessagePack.PackerConfig()
                    .newBufferPacker();
        byte[] msg = new byte[] {
                    -127, -92, 116, 121, 112, 101, -92, 112, 105, 110, 103};
        try {
            packer.writePayload(msg);
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println("Done.");
    }
}

This results in:

Exception in thread "main" java.lang.NullPointerException
    at org.msgpack.core.MessagePacker.writePayload(MessagePacker.java:733)
    at org.msgpack.core.MessagePacker.writePayload(MessagePacker.java:717)
    at Main.main(Main.java:13)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

I simply want to write raw msgpack bytes to a packer, without any previous header. The bytes already contain the map header.