patch 8.2.4581: null types not fully tested

Problem:    Null types not fully tested.
Solution:   Add some more tests using null types.
diff --git a/src/version.c b/src/version.c
index fe974f6..fd63279 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4581,
+/**/
     4580,
 /**/
     4579,