[Sqlalchemy-tickets] Issue #3841: Enum validation causes problems with values not in Enum (zzzeek/sqlalchemy)

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

New issue 3841: Enum validation causes problems with values not in Enum
https://bitbucket.org/zzzeek/sqlalchemy/issues/3841/enum-validation-causes-problems-with

Christian:

After upgrading from 1.0 to 1.1.3, i get this error:

```
  File "/home/xxx/.venv/xxx/lib/python2.7/site-packages/sqlalchemy/sql/sqltypes.py", line 1317, in _object_value_for_elem
    '"%s" is not among the defined enum values' % elem)
LookupError: "" is not among the defined enum values
```

MySQL allows to insert data, that is not in the Enum.

Test Case
```
#!python

import unittest
from sqlalchemy import (Column, Integer, Enum)
from sqlalchemy.ext.declarative import declarative_base
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = ("mysql://root:develop@localhost/test123")
db = SQLAlchemy(app)

Base = declarative_base()

class Test(db.Model):
    __tablename__ = 'test'
    id = Column(Integer, primary_key=True, nullable=False)

    default = Column(Enum('VALUE1','VALUE2'))

db.drop_all()
db.create_all()

class TestSelfEnum(unittest.TestCase):

    def test_enum(self):
        db.session.add(Test(default="VALUE1"))
        db.engine.execute('INSERT INTO test(`default`) VALUES("")')
        db.session.commit()
        result = db.session.query(Test).all()
```