Auth.getOAuth2Token() returns null

I am using dropbox-sdk-java v2 for android. If I try to authenticate the flow from browser, I always get NULL. Issues related to this kind of question are #71 and #161 and they are already closed but none helpful.
My manifest looks like:
`android:name="com.dropbox.core.android.AuthActivity"`
`android:configChanges="orientation|keyboard"`
`android:screenOrientation="portrait"`
`android:launchMode="singleTask"`
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Start with Auth.getOAuth2Token() and the Android AuthActivity manifest entry shown in the issue. Reproduce the browser authentication flow on Android and compare the callback configuration with the related issues #71 and #161. Done means identifying why the method returns null and documenting or fixing the callback behavior.

由索引模型根据 Issue 内容生成。