Android Studio中在onDestroy销毁定时器的时候,返回会报空指针异常

java.lang.RuntimeException: Unable to destroy activity {com.beidou/com.beidou.loginpage.register.view.RegisterActivity}: java.lang.NullPointerException
                                                              at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3483)
                                                              at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3501)
                                                              at android.app.ActivityThread.access$1400(ActivityThread.java:135)
                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1249)
                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                              at android.os.Looper.loop(Looper.java:136)
                                                              at android.app.ActivityThread.main(ActivityThread.java:5001)
                                                              at java.lang.reflect.Method.invokeNative(Native Method)
                                                              at java.lang.reflect.Method.invoke(Method.java:515)
                                                              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
                                                              at dalvik.system.NativeStart.main(Native Method)
                                                           Caused by: java.lang.NullPointerException
                                                              at com.beidou.loginpage.register.view.RegisterActivity.onDestroy(RegisterActivity.java:343)                                                              at android.app.Activity.performDestroy(Activity.java:5403)
                                                              at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1117)
                                                              at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3470)
                                                              at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3501) 
                                                              at android.app.ActivityThread.access$1400(ActivityThread.java:135) 
                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1249) 
                                                              at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                              at android.os.Looper.loop(Looper.java:136) 
                                                              at android.app.ActivityThread.main(ActivityThread.java:5001) 
                                                              at java.lang.reflect.Method.invokeNative(Native Method) 
                                                              at java.lang.reflect.Method.invoke(Method.java:515) 
                                                              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609) 
                                                              at dalvik.system.NativeStart.main(Native Method)