patch 8.2.2133: Vim9: checking for a non-empty string is too strict

Problem:    Vim9: checking for a non-empty string is too strict.
Solution:   Check for any string. (closes #7447)
diff --git a/src/errors.h b/src/errors.h
index b8ec986..30f0dc5 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -313,3 +313,5 @@
 	INIT(= N_("E1140: For argument must be a sequence of lists"));
 EXTERN char e_indexable_type_required[]
 	INIT(= N_("E1141: Indexable type required"));
+EXTERN char e_non_empty_string_required[]
+	INIT(= N_("E1142: Non-empty string required"));