@Override void addSources(double weight,Map<Source,SourceNode> sources) {
        SourceNode existing=sources.get(source);
        if (existing!=null)
            existing.increaseScore(weight*getScore());
        else
            sources.put(source,new SourceNode(source,weight*getScore()));
    }
Returns the source of this node
container-search/src/main/java/com/yahoo/search/intent/model/SourceNode.java