diff --git a/src/main/java/org/RI/P2/Indexer.java b/src/main/java/org/RI/P2/Indexer.java
index 3d2af20..0e66c72 100644
--- a/src/main/java/org/RI/P2/Indexer.java
+++ b/src/main/java/org/RI/P2/Indexer.java
@@ -80,11 +80,13 @@ public class Indexer {
         Document doc = new Document();
         doc.add(new StringField("document_id", paper.paper_id, Field.Store.YES));
         doc.add(new TextField("title", paper.metadata.title, Field.Store.YES));
+        StringBuilder authors = new StringBuilder();
         for (Author author : paper.metadata.authors) {
             String authorName = author.first + " " + author.middle + " " + author.last;
             authorName = authorName.replaceAll("\\p{P}", "");
-            doc.add(new TextField("authors", authorName, Field.Store.YES));
+            authors.append(authorName);
         }
+        doc.add(new TextField("authors", authors.toString(), Field.Store.YES));
         StringBuilder fullAbstract = new StringBuilder();
         for (Abstract abstract_ : paper.abstract_) {
             fullAbstract.append(abstract_.text);
@@ -102,7 +104,9 @@ public class Indexer {
         createIndex();
         for (File file : files) {
             Paper paper = parseJSONFile(file);
-            addDocument(paper);
+            if (paper != null) {
+                addDocument(paper);
+            }
         }
         commitChanges();
     }