我们在测试demo看门狗功能闪退，操作系统为Android 7.1，错误信息：
java.lang.NullPointerException: Attempt to invoke virtual method ‘boolean com.firefly.api.FireflyApi.watchDogEnable(boolean)’ on a null object reference
at com.uartdemo.myapplication.hardware.TestHardware.onListItemClick(TestHardware.java:100)
at android.app.ListActivity$2.onItemClick(ListActivity.java:319)
at android.widget.AdapterView.performItemClick(AdapterView.java:310)
at android.widget.AbsListView.performItemClick(AbsListView.java:1164)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3132)
at android.widget.AbsListView.onTouchUp(AbsListView.java:4059)
空指针请问是什么原因