MDEV-24585 Assertion `je->s.cs == nice_js->charset()' failed in json_nice.

We should set the charset in
Item_func_json_format::fix_length_and_dec().

mysql-test/r/func_json.result

@@ -934,5 +934,11 @@ CAST(JSON_EXTRACT('{"x":false}', '$.x') AS DECIMAL) AS cd;
 cf	cd
 0	0
 #
+# MDEV-24585 Assertion `je->s.cs == nice_js->charset()' failed in json_nice.
+#
+SELECT JSON_REPLACE( JSON_DETAILED('["x"]'), '$.a', 'xx' );
+JSON_REPLACE( JSON_DETAILED('["x"]'), '$.a', 'xx' )
+["x"]
+#
 # End of 10.2 tests
 #

mysql-test/t/func_json.test

@@ -554,6 +554,12 @@ SELECT
   CAST(JSON_EXTRACT('{"x":false}', '$.x') AS DECIMAL) AS cd;
 
 
+--echo #
+--echo # MDEV-24585 Assertion `je->s.cs == nice_js->charset()' failed in json_nice.
+--echo #
+
+SELECT JSON_REPLACE( JSON_DETAILED('["x"]'), '$.a', 'xx' );
+
 --echo #
 --echo # End of 10.2 tests
 --echo #

sql/item_jsonfunc.cc

@@ -3534,6 +3534,7 @@ const char *Item_func_json_format::func_name() const
 bool Item_func_json_format::fix_length_and_dec()
 {
   decimals= 0;
+  collation.set(args[0]->collation);
   max_length= args[0]->max_length;
   maybe_null= 1;
   return FALSE;