Unicode error happens only for update from admin.py

Question

I bumped into this error, when I am updating the column (datatype text) on django admin.py.

unicode error happens only for update
 '\\xF0\\x9F\\x98\\xA1' for column 'object_repr' at row 1

This is because of UTF-8 problem,When I use 4byte character it happens.

The text data(it uses 4byte characters) is already stored in mysql database and definition of table is like this below.

show create table tweet_corpus;
+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table        | Create Table                                                                                                                                                                                                    |
+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tweet_corpus | CREATE TABLE `tweet_corpus` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `text` text,
  `manual_judge` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2471024 DEFAULT CHARSET=utf8mb4 |
+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

And connection from django to mysql is utf8mb4

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'corpustest',
        'USER': 'root',
        'PASSWORD': 'mysql',
        'HOST': '127.0.0.1',
        'PORT': '3306',
        'OPTIONS': {
            'charset': 'utf8mb4',
        }
    }
}

my admin.py is like this ,

class CorpusAdmin(admin.ModelAdmin):
    list_display = ['text','manual_judge']
    search_fields = ['text','manual_judge']
    list_editable = ['manual_judge']    
    def _issues(self,row):
        return row.id

Is there any place I need to check???