Setting just <fieldtype>(default=None) does not work - but should
Disagree, fields are not-null by default, and there is no "sentinel" value for `default` -- in other words, the default is (by default) None.

All you really need to specify is:

`last_logged_on = DateTimeField(null=True)`


New user here and just ran into this one which surprised me.

Setting a Field default to None does not work by itself when creating  a Model row because there is an implicit null=False.
```
class User(BaseModel):
    name = TextField()
    # last_logged_on = DateTimeField(default=None)  # This will not work when created using default ( i.e. it was omitted)!
    last_logged_on = DateTimeField(null=True, default=None)   # this will work

```

I was  taught that Explicit should ALWAYS override Implicit so I would expect my Field argument (command) to set a field to None to cause Peewee to do everything necessary to make that happen without another argument.

Requiring both is counterintuitive.