The server does not detect changes in NULL-ability of system table columns

#

# Modify the column 'definer' mostly preserving the data type,

# changing only NOT NULL DEFAULT '' to DEFAULT NULL.

#

ALTER TABLE mysql.proc MODIFY definer 

  varchar(384) CHARACTER SET utf8mb3 COLLATE utf8mb3_bin DEFAULT NULL;

#

# The procedure gets created without problems.

# However, it's not later possible to execute this procedure.

# The CREATE should rather fail with ER_CANNOT_LOAD_FROM_TABLE_V2.

#

DELIMITER $$;

CREATE PROCEDURE p1()

BEGIN

  SELECT 'p1';

END;

$$

DELIMITER ;$$

#

# Notice, its definer is set to NULL instead of 'root@localhost'.

#

SELECT definer FROM mysql.proc WHERE db='test' AND name='p1';

#

# The CALL statement with a very confusing error:

# query 'CALL p1' failed: ER_NO_SUCH_USER (1449):

#   The user specified as a definer (''@'') does not exist

#

CALL p1;

# Clean-up

DROP PROCEDURE p1;

ALTER TABLE mysql.proc MODIFY definer 

  varchar(384) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL DEFAULT '';

 store_failed= store_failed ||

      table->field[MYSQL_PROC_FIELD_DEFINER]->

        store(definer, system_charset_info);

typedef struct st_table_field_type

{

  LEX_CSTRING name;

  LEX_CSTRING type;

  LEX_CSTRING cset;

} TABLE_FIELD_TYPE;