[CSV-121] Exception that the header contains duplicate names when the column names are empty. Add a test that shows that TWO missing header is not OK.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1602168 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -649,6 +649,12 @@ public class CSVParserTest {
         assertFalse(records.hasNext());
     }
 
+    @Test(expected=IllegalArgumentException.class)
+    public void testHeadersMissingException() throws Exception {
+        final Reader in = new StringReader("a,,c,,d\n1,2,3,4\nx,y,z,zz");
+        CSVFormat.DEFAULT.withHeader().parse(in).iterator();
+    }
+
     @Test
     public void testHeaderComment() throws Exception {
         final Reader in = new StringReader("# comment\na,b,c\n1,2,3\nx,y,z");