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