如何获取java.lang.NullPointerException?

当我找到答案时,我会把自己踢得遍体鳞伤,但我很困惑,所以:

我得到了一个 NullPointerException (一些)用户在尝试访问OneDrive时报告。当然,我自己无法复制。我正在使用Microsoft的OneDrive SDK。 FileListItem 是我正在尝试填充的类 success() SDK回调的方法。错误的位置来自Google Play开发者控制台错误详细信息中的堆栈跟踪。

final ICallback<IItemCollectionPage> callback = new ICallback<IItemCollectionPage>() {
    @Override
    public void success(final IItemCollectionPage result) {
        for (Item child : result.getCurrentPage()) {
            FileListItem item = new FileListItem();
            item.name = child.name;
            if (child.parentReference != null) {
                item.sourcePath = child.parentReference.path;  // java.lang.NullPointerException
            }
            ...

所以 child 来自 for 循环遍历传递给的(可能有效)列表 成功 ,它不会崩溃 child.name 和 child.parentReference != null .

我的问题是如果 item 是我刚刚创建的有效对象,并且 child.parentReference!=无效的 ,这些用户怎么会得到 空指针异常 ?

已编辑以添加完整堆栈跟踪:

java.lang.NullPointerException: 
  at [myapp].OneDriveProvider$4.success (OneDriveProvider.java:183)
  at [myapp].OneDriveProvider$4.success (OneDriveProvider.java:176)
  at com.onedrive.sdk.concurrency.DefaultExecutors$1.run (DefaultExecutors.java:88)
  at com.onedrive.sdk.concurrency.SynchronousExecutor$1.onPostExecute (SynchronousExecutor.java:54)
  at com.onedrive.sdk.concurrency.SynchronousExecutor$1.onPostExecute (SynchronousExecutor.java:46)
  at android.os.AsyncTask.finish (AsyncTask.java:755)
  at android.os.AsyncTask.access$900 (AsyncTask.java:192)
  at android.os.AsyncTask$InternalHandler.handleMessage (AsyncTask.java:772)
  at android.os.Handler.dispatchMessage (Handler.java:107)
  at android.os.Looper.loop (Looper.java:214)
  at android.app.ActivityThread.main (ActivityThread.java:7397)
  at java.lang.reflect.Method.invoke (Native Method)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:492)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:935)