Lucene.Net.Analysis.ChainedFilter.GetDISI C# (CSharp) Method

        private DocIdSetIterator GetDISI(Filter filter, IndexReader reader)
        {
            DocIdSet docIdSet = filter.GetDocIdSet(reader);
            if (docIdSet == null)
            {
                return DocIdSet.EMPTY_DOCIDSET.Iterator();
            }
            else
            {
                DocIdSetIterator iter = docIdSet.Iterator();
                if (iter == null)
                {
                    return DocIdSet.EMPTY_DOCIDSET.Iterator();
                }
                else
                {
                    return iter;
                }
            }
        }