insert_many() does not generate NULL values for fields with null=True
Thanks, this is fixed now. @coleifer Thanks! Could you release a new version with this fix? :) 3.14.3 Hey Im still having this issue, and i dont know how to solve it.  Works fine for me:

```python
class Reg(Model):
    key = TextField()
    value = IntegerField(null=True)
    class Meta:
        database = db

db.create_tables([Reg])

l1 = [{'key': 'k1', 'value': None}, {'key': 'k2'}, {'key': 'k3', 'value': 3}]
l2 = [{'key': 'k4'}, {'key': 'k5', 'value': None}, {'key': 'k6', 'value': 6}]

Reg.insert_many(l1, fields=['key', 'value']).execute()
Reg.insert_many(l2, fields=['key', 'value']).execute()

for r in Reg.select().order_by(Reg.key):
    print(r.key, r.value)
# k1 None
# k2 None
# k3 3
# k4 None
# k5 None
# k6 6
```

If you don't specify `fields` it will just infer the fields you want from the *first* dict in the list of rows to insert. Alternatively, you can of course provide row tuples.

http://docs.peewee-orm.com/en/latest/peewee/querying.html#bulk-inserts You re rigth, the error was mine.
Snippet with error.
```python
import peewee

db = peewee.SqliteDatabase('people.db')


class Model(peewee.Model):
    name = peewee.CharField()
    x = peewee.IntegerField(null=True)

    class Meta:
        database = db


db.connect()
db.create_tables([Model])
query = Model.insert_many([{"name": "foo", "x": None}, {"name":"bar"}])
query.execute()
```
In a workaround i have to use callable, because of `default=None` is ommited:
```python
class Model(peewee.Model):
    name = peewee.CharField()
    x = peewee.IntegerField(null=True, default=lambda: None)

    class Meta:
        database = db
```

