[Sqlalchemy-tickets] Issue #3159: cant insert NULL into a json column if column is present (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3159: cant insert NULL into a json column if column is present
https://bitbucket.org/zzzeek/sqlalchemy/issue/3159/cant-insert-null-into-a-json-column-if

Mike Bayer:

the serializer grabs None if it is present.   for backwards compat we should support null() which currently also blows up:


```
#!python

from sqlalchemy import create_engine, Column, Table, MetaData, func, select, null
from sqlalchemy.dialects.postgresql import JSON

e = create_engine("postgresql://scott:tiger@localhost/test", echo='debug')
c = e.connect()
t = c.begin()

table = Table('json_test', MetaData(), Column('data', JSON))
table.create(c)

c.execute(table.insert(), [{"data": {"foo": "bar"}}, {"data": None}])

assert c.scalar(
    select([func.count('*')]).
    select_from(table).where(table.c.data == null()))


# probable workaround, also fails to invoke
#c.execute(table.insert(), [{"data": {"foo": "bar"}}, {"data": null()}])

```