final int aIdx = extraFieldNames.indexOf("aaa_field");
        final int mIdx = extraFieldNames.indexOf("mmm_field");
        final int zIdx = extraFieldNames.indexOf("zzz_field");
        assertTrue(aIdx < mIdx);
        assertTrue(mIdx < zIdx);
    }

    @Test
    public void test_registerExtraFields_nullDoc_showsConfigFields() throws Exception {

		if a.oi.ModTime.Equal(b.oi.ModTime) {
			// On tiebreak, select the lowest pool index.
			return a.zIdx < b.zIdx
		}
		return a.oi.ModTime.After(b.oi.ModTime)
	})

	for _, res := range results {
		err := res.err
		if err == nil {
			return res.oi, res.zIdx, nil
		}
		if !isErrObjectNotFound(err) && !isErrVersionNotFound(err) {