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Ensure that @key is non-%NULL on g_settings_reset(). It turns out that using g_settings_reset() with %NULL key (although invalid as per the API documentation and not possible via bindings) accidentally produces the same effect as the _reset_all() API that we are about to add. Add the standard precondition checks to prevent that from happening. https://bugzilla.gnome.org/show_bug.cgi?id=744678
ca037538