comments: it took me a few minutes to figure out why this was correct

git-svn-id: https://svn.apache.org/repos/asf/lucene/solr/trunk@583359 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/solr/search/SolrIndexSearcher.java

@@ -729,6 +729,8 @@ public class SolrIndexSearcher extends Searcher implements SolrInfoMBean {
           if (superset != null) {
             // check that the cache entry has scores recorded if we need them
             if ((flags & GET_SCORES)==0 || superset.hasScores()) {
+              // NOTE: subset() returns null if the DocList has fewer docs than
+              // requested
               out.docList = superset.subset(offset,len);
             }
           }