[Sqlalchemy-tickets] Issue #3830: Column(JSON, default=None) defaults to SQL NULL in 1.1 instead of JSON null (zzzeek/sqlalchemy)

[Adrian <iss...@bi...>]

New issue 3830: Column(JSON, default=None) defaults to SQL NULL in 1.1 instead of JSON null
https://bitbucket.org/zzzeek/sqlalchemy/issues/3830/column-json-default-none-defaults-to-sql

Adrian:

```python
from datetime import datetime, date

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.dialects.postgresql import JSON


Base = declarative_base()


class Foo(Base):
    __tablename__ = 'foo'
    id = Column(Integer, primary_key=True)
    json = Column(JSON, nullable=False, default=None)

e = create_engine('postgresql:///test', echo=True)
Base.metadata.create_all(e)
s = Session(e)


s.add(Foo())
s.flush()
```

This fails with the NOT NULL being violated. Using `default=JSON.NULL` works but unless I misunderstand [the docs](http://docs.sqlalchemy.org/en/rel_1_1/changelog/migration_11.html#json-null-is-inserted-as-expected-with-orm-operations-regardless-of-column-default-present) I shouldn't get a SQL NULL there.