Message event type does not support bot-generated messages

[JadedEvan]

The current implementation for the Message variant for the EventCallbackType does not support messages that were sent via Slackbots. The current enum implementation requires a user attribute which does not exist in this type of callback event - you can see the documentation in the bot_message docs. Instead of user you have username.

As an example - this payload will fail when deserialized

{
    "token": "some-token",
    "team_id": "XVFU4HSB0",
    "api_app_id": "A0454AVL9L0",
    "event": {
        "type": "message",
        "subtype": "bot_message",
        "text": "message text",
        "ts": "1665341482.399349",
        "username": "My Slackbot",
        "bot_id": "B04488SU0P8",
        "app_id": "A088TG2RTDF",
        "channel": "C044T73TB17",
        "event_ts": "1665341482.399349",
        "channel_type": "channel"
    },
    "type": "event_callback",
    "event_id": "Ev0464MAU18R",
    "event_time": 1665341482,
    "authorizations": [
        {
            "enterprise_id": null,
            "team_id": "TCFU9GHJR",
            "user_id": "U044ELFUMMG",
            "is_bot": true,
            "is_enterprise_install": false
        }
    ],
    "is_ext_shared_channel": false,
    "event_context": "4-eyJldCI6Im1lc3NhZ2UiLCJ0aWQiOiJUQ0ZVOUhTQjAiLCJhaWQiOiJBMDQ1NEFWTDlMMCIsImNpZCI6IkMwNDRUNzNUQjE3In0"
}