Make sure an unmapped header returns null

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1498003 13f79535-47bb-0310-9956-ffa450edef68

Author: britter

src/test/java/org/apache/commons/csv/CSVRecordTest.java

@@ -18,6 +18,7 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
 import java.util.HashMap;
@@ -69,6 +70,11 @@ public void testGetStringInconsistentRecord() {
         recordWithHeader.get("fourth");
     }
 
+    @Test
+    public void testGetUnmapped() {
+        assertNull(recordWithHeader.get("fourth"));
+    }
+
     @Test
     public void testIsConsistent() {
         assertTrue(record.isConsistent());