Android full backup: "file.xml is not in an included path"

I've created backup rules file just like in example https://developer.android.com/guide/topics/data/autobackup:

<?xml version="1.0" encoding="utf-8"?>
<full-backup-content xmlns:android="http://schemas.android.com/apk/res/android">
    <include
        domain="sharedpref"
        path="." />
    <exclude
        domain="sharedpref"
        path="nonceStorage.xml" />
    <exclude
        domain="sharedpref"
        path="localStorage.xml" />
</full-backup-content>

and Android Studio say's that there are errors:

Error:(8, 15) `nonceStorage.xml` is not in an included path [FullBackupContent]
Error:(11, 15) `localStorage.xml` is not in an included path [FullBackupContent]

Error message is totally uninformative and not googleable (almost all words are very short). Can anyone explain,what does this *** want from me? How to fix this issue?

from Android full backup: "file.xml is not in an included path"