@Override
    public String getIndexName() {
        if (getItemCount() == 0) {
            return "";
        } else {
            return ((IndexedItem) getItem(0)).getIndexName();
        }
    }
An immutable and'ing of a collection of sub-expressions. It does not extend
AndItem to avoid code using instanceof handling it as an AndItem.

@author Steinar Knutsen
container-search/src/main/java/com/yahoo/prelude/query/AndSegmentItem.java