写文件空指针异常

[openproject]

--------- beginning of /dev/log/main --------- beginning of /dev/log/system FATAL EXCEPTION: main java.lang.NullPointerException at com.tianxia.app.floworld.utils.FileUtils.writeTextFile(FileUtils.java:54) at com.tianxia.app.floworld.cache.ConfigCache.setUrlCache(ConfigCache.java:60) at com.tianxia.app.floworld.discuss.DiscussTabActivity$1.onSuccess(DiscussTabActivity.java:85) at com.tianxia.lib.baseworld.sync.http.AsyncHttpResponseHandler.handleSuccessMessage(AsyncHttpResponseHandler.java:156) at com.tianxia.lib.baseworld.sync.http.AsyncHttpResponseHandler.handleMessage(AsyncHttpResponseHandler.java:169) at com.tianxia.lib.baseworld.sync.http.AsyncHttpResponseHandler$1.handleMessage(AsyncHttpResponseHandler.java:85) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:150) at android.app.ActivityThread.main(ActivityThread.java:4293) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:507) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607) at dalvik.system.NativeStart.main(Native Method) 2012-05-07 13:39:12 2.3.4 HTC Sensation Z710e