'What is the type returned when the backend introspects a BooleanField?
The `field` argument may be used to give further details of the field
to be introspected.
The return value from this function is compared by tests against actual
introspection results; it should provide expectations, not run an
introspection itself.'

def introspected_boolean_field_type(self, field=None):

    if (self.can_introspect_null and field and field.null):
        return 'NullBooleanField'
    return 'BooleanField'
