Adding calculated attribute to the scheme

[Bu3a3a]

Hi!
I'm trying to add a calculated field to the scheme using @post_dump:

from marshmallow_jsonapi import Schema as JSONApiSchema, fields


class MyScheme(JSONApiSchema):
    id = fields.Int(required=False)
    is_deleted = fields.Bool(required=True)
    is_enabled = fields.Bool(required=True)
    is_active = fields.Bool(required=False)

    class Meta:
        type_ = 'my_model'

    @post_dump
    def is_active(self, data):
        data['is_active'] = bool(not data['is_deleted'] and data['is_enabled'] ) 

I'm getting this error:

.../python3.7/site-packages/marshmallow_jsonapi/schema.py", line 355, in format_item
    attribute = attributes[field_name]
KeyError: 'is_active'

Is there a way to make it with marshmallow-jsonapi?