Ошибка в Django Model и Serializer - (1048, "Column 'dso_id' cannot be null")

Я пытаюсь создать профиль пользователя, я чувствую, что у меня все правильно, но все равно он не регистрируется. Вы видите мою кодовую базу ниже, пожалуйста, помогите

Что я сделал:

Models.py:

class UserManager(BaseUserManager):
    def create_user(self, username, email, name, address,roleId,customerId,dso password=None,):
        if username is None:
            raise TypeError('User should have a userame')
        if email is None:
            raise TypeError('Users should have a Email')
        
        user = self.model(username=username , email = self.normalize_email(email))
        user.set_password(password)
        user.save()
        return user
    
    def create_superuser(self, username, email, password=None):
        if password is None:
            raise TypeError('User should have a password')
       
        user=self.create_user(username,email,password,)
        user.is_superuser = True
        user.is_staff = True
        user.save()
        return user

class User(models.Model):
    dso = models.ForeignKey(Dso,related_name='dso',default=NULL,blank=False,on_delete=models.CASCADE)
    name = models.CharField(max_length=70, blank=False, default='')
    email = models.EmailField(max_length=70, blank=False, default='')
    password = models.CharField(max_length=70, blank=False, default='')
    address = models.CharField(max_length=70, blank=False, default='')
    roleId = models.IntegerField(blank=False, default='1')
    isActive = models.BooleanField(blank=False, default=True)
    customerId = models.CharField(max_length=70, blank=False, default='')
    
    dateJoined = models.DateTimeField(auto_now_add=False, blank=False, default=NULL)

    @property
    def energy_data(self):
        energydata = EnergyData.objects.filter(customerId=self.customerId).first()
        return energydata

Serializers.py:

class RegisterSerializer(serializers.ModelSerializer):
    password = serializers.CharField(max_length = 68, min_length=6, write_only = True)
    
    class Meta:
        model=User
        fields=['email','username','password','name','address','customerId', 
                  'dso', 'roleId']
    
    def validate(self, attrs):
        email = attrs.get('email', '')
        username = attrs.get('username', '')

        if not len(username) >= 4:
            raise serializers.ValidationError('Username must be morethan 4 letters or characters')
        return attrs

    def create(self, validated_data):
        return User.objects.create_user(**validated_data)

Views.py:

class RegisterView(generics.GenericAPIView):

    serializer_class= RegisterSerializer 
    def post(self, request):
        user = request.data
        serializer = self.serializer_class(data=user)
        serializer.is_valid(raise_exception=True)
        serializer.save()
        user_data = serializer.data

        user= User.objects.get(email=user_data['email'])

        token = RefreshToken.for_user(user).access_token

        current_site = get_current_site(request).domain

        relativeLink = reverse('email-verify')
        
        absolute_url = 'http://'+current_site+relativeLink+"?token="+str(token)

        email_body= 'Hi '+ user.username + ' Use this link below to verify your email \n'+ absolute_url

        data = {'email_subject': 'Verify Your Email', 'email_body': email_body , 'to_email': user.email}

        Util.send_email(data)

        return Response(user_data, status = status.HTTP_201_CREATED)

URL Path:

path('register/', RegisterView.as_view(), name="register" )

Когда я делаю это и пытаюсь проверить, я получаю ошибку, '(1048, "Column 'dso_id' cannot be null")'

Пожалуйста, помогите, так как я новичок в django rest framework.

dso = models.ForeignKey(Dso,related_name='dso',default=NULL,blank=False,on_delete=models.CASCADE)

dso = models.ForeignKey(Dso,related_name='dso',default=NULL, blank=True, null=True, on_delete=models.CASCADE)