[Sqlalchemy-tickets] Issue #4031: eval_none logic isn't resolving col to prop (zzzeek/sqlalchemy)

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

New issue 4031: eval_none logic isn't resolving col to prop
https://bitbucket.org/zzzeek/sqlalchemy/issues/4031/eval_none-logic-isnt-resolving-col-to-prop

Michael Bayer:

```
#!python

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class A(Base):
    __tablename__ = 'a'

    id = Column(Integer, primary_key=True)
    column1 = Column('column1', JSON, nullable=False)
    _column2 = Column('column2', JSON, nullable=False)

e = create_engine("postgresql://scott:tiger@localhost/test", echo=True)
Base.metadata.drop_all(e)
Base.metadata.create_all(e)

session = Session(e)

# Succeeds
session.add(A(column1=[], _column2=[]))
session.flush()

# Succeeds
session.add(A(column1=None, _column2=[]))
session.flush()

# Fails with integrity error
session.add(A(column1=[], _column2=None))
session.flush()




```

this would be the patch but need to confirm key is always present in _columntoproperty in this context:

```
#!diff


diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 1042442..68103d2 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -2020,7 +2020,7 @@ class Mapper(InspectionAttr):
             (
                 table,
                 frozenset(
-                    col.key for col in columns
+                    self._columntoproperty[col].key for col in columns
                     if col.type.should_evaluate_none
                 )
             )

```