MDEV-12363 Assertion `0' failed in...

MDEV-12363 Assertion `0' failed in Type_handler_string_result::make_sort_key(uchar*, Item*, const SORT_FIELD_ATTR*, Sort_param*).

        maybe_null wasn't properly set for Item_json_func_keys.

mysql-test/r/func_json.result

@@ -636,3 +636,9 @@ JSON_SEARCH('{"foo":"bar"}', 'all' , @str, '%', @path)
 SELECT JSON_VALUE('[{"foo": 1},"bar"]', '$[*][0]');
 JSON_VALUE('[{"foo": 1},"bar"]', '$[*][0]')
 bar
+CREATE TABLE t1 (f INT NOT NULL);
+INSERT INTO t1 VALUES (0);
+SELECT JSON_KEYS(f) FROM t1 ORDER BY 1;
+JSON_KEYS(f)
+NULL
+DROP TABLE t1;

mysql-test/t/func_json.test

@@ -287,3 +287,12 @@ SELECT JSON_SEARCH('{"foo":"bar"}', 'all' , @str, '%', @path);
 
 SELECT JSON_VALUE('[{"foo": 1},"bar"]', '$[*][0]');
 
+#
+# MDEV-12363 Assertion `0' failed in Type_handler_string_result::make_sort_key(uchar*, Item*, const SORT_FIELD_ATTR*, Sort_param*)      
+#
+
+CREATE TABLE t1 (f INT NOT NULL);
+INSERT INTO t1 VALUES (0);
+SELECT JSON_KEYS(f) FROM t1 ORDER BY 1;
+DROP TABLE t1;
+

sql/item_jsonfunc.cc

@@ -444,6 +444,7 @@ void Item_func_json_value::fix_length_and_dec()
   collation.set(args[0]->collation);
   max_length= args[0]->max_length;
   path.set_constant_flag(args[1]->const_item());
+  maybe_null= 1;
 }
 
 
@@ -582,6 +583,7 @@ void Item_func_json_unquote::fix_length_and_dec()
 {
   collation.set(&my_charset_utf8_general_ci);
   max_length= args[0]->max_length;
+  maybe_null= 1;
 }
 
 
@@ -683,6 +685,7 @@ void Item_func_json_extract::fix_length_and_dec()
   max_length= args[0]->max_length * (arg_count - 1);
 
   mark_constant_paths(paths, args+1, arg_count-1);
+  maybe_null= 1;
 }
 
 
@@ -884,6 +887,7 @@ void Item_func_json_contains::fix_length_and_dec()
 {
   a2_constant= args[1]->const_item();
   a2_parsed= FALSE;
+  maybe_null= 1;
   if (arg_count > 2)
     path.set_constant_flag(args[2]->const_item());
   Item_int_func::fix_length_and_dec();
@@ -1129,6 +1133,7 @@ void Item_func_json_contains_path::fix_length_and_dec()
 {
   ooa_constant= args[1]->const_item();
   ooa_parsed= FALSE;
+  maybe_null= 1;
   mark_constant_paths(paths, args+2, arg_count-2);
   Item_int_func::fix_length_and_dec();
 }
@@ -2042,6 +2047,7 @@ void Item_func_json_length::fix_length_and_dec()
 {
   if (arg_count > 1)
     path.set_constant_flag(args[1]->const_item());
+  maybe_null= 1;
 }
 
 
@@ -2178,6 +2184,7 @@ void Item_func_json_type::fix_length_and_dec()
 {
   collation.set(&my_charset_utf8_general_ci);
   max_length= 12;
+  maybe_null= 1;
 }
 
 
@@ -2245,6 +2252,7 @@ void Item_func_json_insert::fix_length_and_dec()
   }
 
   fix_char_length_ulonglong(char_length);
+  maybe_null= 1;
 }
 
 
@@ -2491,6 +2499,7 @@ void Item_func_json_remove::fix_length_and_dec()
   max_length= args[0]->max_length;
 
   mark_constant_paths(paths, args+1, arg_count-1);
+  maybe_null= 1;
 }
 
 
@@ -2674,6 +2683,7 @@ void Item_func_json_keys::fix_length_and_dec()
 {
   collation.set(args[0]->collation);
   max_length= args[0]->max_length;
+  maybe_null= 1;
   if (arg_count > 1)
     path.set_constant_flag(args[1]->const_item());
 }
@@ -2815,6 +2825,7 @@ void Item_func_json_search::fix_length_and_dec()
 
   if (arg_count > 4)
     mark_constant_paths(paths, args+4, arg_count-4);
+  maybe_null= 1;
 }
 
 
@@ -2996,6 +3007,7 @@ void Item_func_json_format::fix_length_and_dec()
 {
   decimals= 0;
   max_length= args[0]->max_length;
+  maybe_null= 1;
 }