@Override
    public String getName() {
        return "NOT";
    }
A composite item where the first item is positive and the following
items are negative items where matches should exclude the document should from the result.
The default positive item, if only negatives are added, is TrueItem: Meaning that all documents are matched
except those matching the negative terms added.

@author bratseth
container-search/src/main/java/com/yahoo/prelude/query/NotItem.java