[Sqlalchemy-tickets] Issue #3514: Cannot insert JSON null via bulk_insert_mappings (zzzeek/sqlalchemy)

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

New issue 3514: Cannot insert JSON null via bulk_insert_mappings
https://bitbucket.org/zzzeek/sqlalchemy/issues/3514/cannot-insert-json-null-via

thiefmaster:

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

Base = declarative_base()


class A(Base):
    __tablename__ = 'test_a'

    id = Column(Integer, primary_key=True)
    data = Column(JSON(none_as_null=False), nullable=False)


# e = create_engine('sqlite:///:memory:', echo=True)
e = create_engine('postgresql:///test', echo=True)
Base.metadata.create_all(e)

s = Session(e)
s.bulk_insert_mappings(A, [{'data': 'null'}])
s.bulk_insert_mappings(A, [{'data': None}])
s.commit()
```

output (only relevant parts)

```
2015-08-17 18:34:06,882 INFO sqlalchemy.engine.base.Engine INSERT INTO test_a (data) VALUES (%(data)s) RETURNING test_a.id
2015-08-17 18:34:06,882 INFO sqlalchemy.engine.base.Engine {'data': '"null"'}
2015-08-17 18:34:06,883 INFO sqlalchemy.engine.base.Engine INSERT INTO test_a DEFAULT VALUES RETURNING test_a.id
2015-08-17 18:34:06,883 INFO sqlalchemy.engine.base.Engine {}
```

So the `None` is never converted to a `'null'` but the `'null'` string is converted to `'"null"'`...