output: #fixed code
                                  private static int spawnPacket(Location loc) throws Exception {
          Object world = Reflections.getHandle(loc.getWorld());
          Object crystal = enderCrystalConstructor.newInstance(world);
          setLocation.invoke(crystal, loc.getX(), loc.getY(), loc.getZ(), 0, 0);
          Object packet = spawnEntityConstructor.newInstance(crystal, 51);
          int id = (int) getId.invoke(crystal);
          ids.put(id, packet);
          return id;
      }
input: #vulnerable code 
                                  private static int spawnPacket(Location loc) throws Exception {
          Object world = Reflections.getHandle(loc.getWorld());
          Object crystal = enderCrystalClass.getConstructor(Reflections.getCraftClass("World")).newInstance(world);
          Reflections.getMethod(enderCrystalClass, "setLocation", double.class, double.class, double.class, float.class, float.class).invoke(crystal, loc.getX(), loc.getY(), loc.getZ(), 0, 0);
          Object packet = spawnEntityClass.getConstructor(new Class<?>[]{entityClass, int.class}).newInstance(crystal, 51);
          int id = (int) Reflections.getMethod(enderCrystalClass, "getId").invoke(crystal);
          ids.put(id, packet);
          return id;
      } 
                              #location 6 
                              #vulnerability type NULL_DEREFERENCE