这是我的密码

from rest_framework import serializers
from django.contrib.auth import get_user_model
User = get_user_model()

class UserSerializer(serializers.ModelSerializer):
    username = serializers.Field(source="username", required = False)   
    class Meta:
        model = User
        fields = ('first_name', 'last_name', 'username')

看起来很简单。问题是什么？