Issue #4860 - Fixing test comment

Signed-off-by: Joakim Erdfelt <joakim.erdfelt@gmail.com>

jetty-http/src/test/java/org/eclipse/jetty/http/HttpFieldsTest.java

@@ -749,7 +749,7 @@ public class HttpFieldsTest
         assertThat(fields.size(), is(1));
         ListIterator<HttpField> iter = fields.listIterator();
         iter.next();
-        iter.set(null); // set field to null - null entry in list now
+        iter.set(null); // set field to null - should result in noop
         assertThat(fields.size(), is(0));
         iter.add(null); // attempt to add null entry
         assertThat(fields.size(), is(0));