Nested serialization regression between 1.8.2 and master

[christianbundy]

Checks

• I added a descriptive title to this issue
• I have searched (google, github) for similar issues and couldn't find anything
• I have read and followed the docs and still think this is a bug

Bug

I found a small regression between 1.8.2 and master that broke some tests for me -- I bisected and found that it started with 458f257. Here's the test I used:

from typing import Optional
from pydantic import BaseModel, Field


class Model(BaseModel):
    value: Optional[str]
    nested: Optional[BaseModel]


def test_my_bug():
    assert (
        Model(value=None, nested=Model(value=None)).json(exclude_none=True)
        == '{"nested": {}}'
    )

In 1.8.2, options to json() (like exclude_none) were passed to all nested models, but in master that no longer occurs. Instead, we see:

{ "nested": { "value": null } }

---

In my case, I noticed this because I had two models:

class Model(BaseModel):
    value: Optional[str]

class OuterModel(Model):
    nested: Optional[Model]

    def json(self, **kwargs):
        kwargs.set_default("exclude_none", True)
        return super().json(**kwargs)


# Usage:
OuterModel(nested=Model()).json()

In 1.8.2 this was overridden json() was used on all nested models as well, but in master this is only applied to the outer model. This means that we get { "nested": { "value": null } } when previously we would've gotten { "nested": {} } like above.

[samuelcolvin]

I think this is the same as #3542. If not, let me know and I'll reopen

[christianbundy]

I think when I posted the bug report they were slightly different, but it looks like @PrettyWood pushed another commit to take care of this. Thanks!