output: #fixed code
                                  @Test
      public void testDecodeWithData() throws IOException {
          JacksonJsonSupport jsonSupport = new JacksonJsonSupport();
          jsonSupport.addEventMapping("", "edwald", HashMap.class, Integer.class, String.class);
          PacketDecoder decoder = new PacketDecoder(jsonSupport, ackManager);
  
          Packet packet = decoder.decodePackets(Unpooled.copiedBuffer("5:::{\"name\":\"edwald\",\"args\":[{\"a\": \"b\"},2,\"3\"]}", CharsetUtil.UTF_8), null);
          Assert.assertEquals(PacketType.EVENT, packet.getType());
          Assert.assertEquals("edwald", packet.getName());
  //        Assert.assertEquals(3, packet.getArgs().size());
  //        Map obj = (Map) packet.getArgs().get(0);
  //        Assert.assertEquals("b", obj.get("a"));
  //        Assert.assertEquals(2, packet.getArgs().get(1));
  //        Assert.assertEquals("3", packet.getArgs().get(2));
      }
input: #vulnerable code 
                                  @Test
      public void testDecodeWithData() throws IOException {
          JacksonJsonSupport jsonSupport = new JacksonJsonSupport();
          jsonSupport.addEventMapping("", "edwald", HashMap.class, Integer.class, String.class);
          PacketDecoder decoder = new PacketDecoder(jsonSupport, ackManager);
  
          Packet packet = decoder.decodePacket("5:::{\"name\":\"edwald\",\"args\":[{\"a\": \"b\"},2,\"3\"]}", null);
          Assert.assertEquals(PacketType.EVENT, packet.getType());
          Assert.assertEquals("edwald", packet.getName());
  //        Assert.assertEquals(3, packet.getArgs().size());
  //        Map obj = (Map) packet.getArgs().get(0);
  //        Assert.assertEquals("b", obj.get("a"));
  //        Assert.assertEquals(2, packet.getArgs().get(1));
  //        Assert.assertEquals("3", packet.getArgs().get(2));
      } 
                              #location 8 
                              #vulnerability type NULL_DEREFERENCE