When subclassing a model field, `max_length` cannot be passed as an argument to `self.__init__`

[Robin (Robert) Thomas]

class MyCustomField(models.CharField):
    def __init__(self, *args, **kwargs):
        super().__init__(max_length=60, *args, **kwargs)

class MyModel(models.Model)
    address_state = MyCustomField()

On attempting to migrate, I get:

super().__init__(max_length=60, *args, **kwargs)
TypeError: __init__() got multiple values for keyword argument 'max_length'

Using kwargs[max_length] works just fine. However, the documentation says that max_length should be able to be passed to super().__init__() as an argument:

​https://docs.djangoproject.com/en/2.2/howto/custom-model-fields/#writing-a-field-subclass

Either the documentation is incorrect, or this is a bug.