cm9 official nightly build changelogs

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hi there,
i am installing the official nightly builds from time to time. i use the official nightly build discussion thread over at the rootzwiki forums to check if anything new is out. but i noticed that the changelogs for some nightly builds are empty or just say: "there are no changes made in this nightly". so i was wondering why the cyanogenmod guys are releasing something which change nothing. or am i missing something there?
just wondering...