patch 8.2.1854: Vim9: crash when throwing exception for NULL string

Problem:    Vim9: crash when throwing exception for NULL string. (Dhiraj
            Mishra)
Solution:   Handle NULL string like empty string. (closes #7139)
diff --git a/src/version.c b/src/version.c
index 5aa3cf6..4710689 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1854,
+/**/
     1853,
 /**/
     1852,