我正在尝试将片段实例保存在Activity的onSaveInstanceState中。 `受保护的无效onSaveInstanceState（Bundle outState）{ super.onSaveInstanceState（outState）;
//Save the fragment's instance
getSupportFragmentManager().putFragment(outState, TAG_RATES_AND_FEES, mRatesAndFeesFragment);
}`
但是我在Crashlytics日志中遇到了异常
Fatal Exception: java.lang.NullPointerException: Attempt to read from field 'int android.support.v4.app.Fragment.mIndex' on a null object reference
at android.support.v4.app.FragmentManagerImpl.putFragment(FragmentManager.java:922)
at com.transfast.transfast.v4.activities.TransactionActivity.onSaveInstanceState(TransactionActivity.java:485)
at android.app.Activity.performSaveInstanceState(Activity.java:1555)
at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1392)
at android.app.ActivityThread.callCallActivityOnSaveInstanceState(ActivityThread.java:4941)