编写Android第一行代码的时候，到实战酷欧天气的时候出了一些Bug,打印的日志如下：

wang.bk 2018-03-01 12:25:30

03-01 00:16:15.765 17880-17880/com.example.lab.android.nuc.coolweather E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.lab.android.nuc.coolweather, PID: 17880
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lab.android.nuc.coolweather/com.example.lab.android.nuc.coolweather.Activity.WeatherActivity}: java.lang.NullPointerException: Attempt to read from field 'java.lang.String com.example.lab.android.nuc.coolweather.gson.Basic.cityName' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2793)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:156)
at android.app.ActivityThread.main(ActivityThread.java:6523)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)
Caused by: java.lang.NullPointerException: Attempt to read from field 'java.lang.String com.example.lab.android.nuc.coolweather.gson.Basic.cityName' on a null object reference
at com.example.lab.android.nuc.coolweather.Activity.WeatherActivity.showWeatherInfo(WeatherActivity.java:126)
at com.example.lab.android.nuc.coolweather.Activity.WeatherActivity.onCreate(WeatherActivity.java:74)
at android.app.Activity.performCreate(Activity.java:6915)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2746)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:156)
at android.app.ActivityThread.main(ActivityThread.java:6523)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)

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