[Sqlalchemy-tickets] Issue #3023: inconsistent behavior of nullable with PrimaryKeyConstraint (zzzeek/sqlalchemy)

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

New issue 3023: inconsistent behavior of nullable with PrimaryKeyConstraint
https://bitbucket.org/zzzeek/sqlalchemy/issue/3023/inconsistent-behavior-of-nullable-with

Mike Bayer:

this is fairly egregious, breaks alembic as one might expect

```
#!python

from sqlalchemy import *

m = MetaData()

t1 = Table('t1', m, Column('x', Integer), PrimaryKeyConstraint('x'))

t2 = Table('t2', m, Column('x', Integer, primary_key=True))

assert list(t1.primary_key) == [t1.c.x]

assert list(t2.primary_key) == [t2.c.x]

assert t1.c.x.primary_key
assert t2.c.x.primary_key

assert not t2.c.x.nullable
assert not t1.c.x.nullable
```