#vulnerable code 
                                @Test
    public void testDecodeWithMessageIdAndAck() throws IOException {
        Packet packet = decoder.decodePacket("5:1+::{\"name\":\"tobi\"}", null);
        Assert.assertEquals(PacketType.EVENT, packet.getType());
//        Assert.assertEquals(1, (long)packet.getId());
//        Assert.assertEquals(Packet.ACK_DATA, packet.getAck());
        Assert.assertEquals("tobi", packet.getName());
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testDecodeWithMessageIdAndAck() throws IOException {
        Packet packet = decoder.decodePackets(Unpooled.copiedBuffer("5:1+::{\"name\":\"tobi\"}", CharsetUtil.UTF_8), null);
        Assert.assertEquals(PacketType.EVENT, packet.getType());
//        Assert.assertEquals(1, (long)packet.getId());
//        Assert.assertEquals(Packet.ACK_DATA, packet.getAck());
        Assert.assertEquals("tobi", packet.getName());
    }