Fix for bug: 31976, avoid NullPointerException when adding a document with an single, empty field and term vectors enabled.

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@150655 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/lucene/index/SegmentReader.java

@@ -489,6 +489,9 @@ class SegmentReader extends IndexReader {
       return null;
     
     TermVectorsReader termVectorsReader = getTermVectorsReader();
+    if (termVectorsReader == null)
+      return null;
+    
     return termVectorsReader.get(docNumber, field);
   }
 
@@ -505,6 +508,9 @@ class SegmentReader extends IndexReader {
       return null;
     
     TermVectorsReader termVectorsReader = getTermVectorsReader();
+    if (termVectorsReader == null)
+      return null;
+    
     return termVectorsReader.get(docNumber);
   }
 }

src/java/org/apache/lucene/index/TermVectorsReader.java

@@ -295,6 +295,10 @@ class TermVectorsReader implements Cloneable {
   }
 
   protected Object clone() {
+    
+    if (tvx == null || tvd == null || tvf == null)
+      return null;
+    
     TermVectorsReader clone = null;
     try {
       clone = (TermVectorsReader) super.clone();