fix NPE in citation servlet on empty text field

htroot/api/citation.java

@@ -116,12 +116,14 @@ public class citation {
 
         ArrayList<String> sentences = new ArrayList<String>();
         if (title != null) for (String s: title) if (s.length() > 0) sentences.add(s);
+        if (text != null && !text.isEmpty()) {
             SentenceReader sr = new SentenceReader(text);
             StringBuilder line;
             while (sr.hasNext()) {
                 line = sr.next();
                 if (line.length() > 0) sentences.add(line.toString());
             }
+        }
 
         // for each line make a statistic about the number of occurrences somewhere else
         OrderedScoreMap<String> scores = new OrderedScoreMap<String>(null); // accumulates scores for citating urls