MDEV-16174 Assertion `0' failed in...

MDEV-16174 Assertion `0' failed in Type_handler_string_result::make_sort_key(uchar*, Item*, const SORT_FIELD_ATTR*, Sort_param*)

maybe_null should be always set to TRUE in
Item_func_json_array_append::fix_length_and_dec()

mysql-test/r/func_json.result

@@ -810,3 +810,17 @@ SET @`json` := NULL, @`value` := NULL;
 SELECT JSON_MERGE('[1]', '[]');
 JSON_MERGE('[1]', '[]')
 [1]
+#
+# MDEV-16174 Assertion `0' failed in Type_handler_string_result::
+#       make_sort_key(uchar*, Item*, const SORT_FIELD_ATTR*, Sort_param*)
+#
+SET sql_mode='';
+CREATE TABLE t1 (fld varchar(16) NOT NULL);
+CREATE TABLE t2 SELECT JSON_ARRAY_INSERT(fld, '$.[0]', '0') FROM t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `JSON_ARRAY_INSERT(fld, '$.[0]', '0')` varchar(25) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1, t2;
+SET sql_mode=default;

mysql-test/t/func_json.test

@@ -468,3 +468,16 @@ SET @`json` := NULL, @`value` := NULL;
 --echo #
 
 SELECT JSON_MERGE('[1]', '[]');
+
+--echo #
+--echo # MDEV-16174 Assertion `0' failed in Type_handler_string_result::
+--echo #       make_sort_key(uchar*, Item*, const SORT_FIELD_ATTR*, Sort_param*)
+--echo #
+
+SET sql_mode='';
+CREATE TABLE t1 (fld varchar(16) NOT NULL);
+CREATE TABLE t2 SELECT JSON_ARRAY_INSERT(fld, '$.[0]', '0') FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t1, t2;
+SET sql_mode=default;
+

sql/item_jsonfunc.cc

@@ -1562,6 +1562,7 @@ bool Item_func_json_array_append::fix_length_and_dec()
   }
 
   fix_char_length_ulonglong(char_length);
+  maybe_null= 1;
   return FALSE;
 }