public Item removeItem(int index) {
        Item removed = super.removeItem(index);

        if (index == 0) { // Don't make the first negative the positive
            insertTrueFirstItem();
        }
        return removed;
    }
Convenience method for adding a positive item.
If a positive item is already present
the positive item becomes an AndItem with the items added
container-search/src/main/java/com/yahoo/prelude/query/NotItem.java