ForeignKey object returns null after relay.ClientIDMutation

* **What is the current behavior?**

ForeignKey object returns null after `relay.ClientIDMutation` although the related object is successfully created.

```
{
"data": {
"createUser": {
"user": {
"address": null
}
}
}
}
```

CreateUser Mutation code will look something similar to this
```
class CreateUser(relay.ClientIDMutation):
class Input:
address = Field(AddressInput, required=False)

user = Field(User)

@classmethod
def mutate_and_get_payload(cls, root, info, **input):
address_payload = input.get('address')
address_obj = AddressModel.objects.create(**address_payload)

user = UserModel.objects.create_user(address=address_obj)

return CreateUser(user=user)
```

* **What is the expected behavior?**
```
{
"data": {
"createUser": {
"user": {
"address": {
"address1": "123 Testing Address St."
}
}
}
}
}
```

* **Please tell us about your environment:**

- Version: 2.13.0
- Platform: django 3.1.2