Custom Attribute Panicked:Unsupported Argument Type

Hello,

I'm running into this error when using enum_dispatch.

use undo::{Action, History, Merged};
use enum_dispatch::enum_dispatch;

pub struct AppState{
    names: Vec<String>
}

#[enum_dispatch(AppActionTest)]
pub trait AppAction{
    fn apply(&mut self, target: &mut AppState) -> Result<(), String>;

    fn undo(&mut self, target: &mut AppState) -> Result<(), String>;

    fn redo(&mut self, target: &mut AppState) -> Result<(), String> {
        self.apply(target)
    }

    fn merge(&mut self, _: &mut AppActionTest) -> Merged {
        Merged::No
    }
}

pub struct AddMask;
impl Action for AddMask{
    type Target = AppState;
    type Output = ();
    type Error = String;
    fn apply(&mut self, target: &mut AppState) -> Result<(), String>{
        dbg!("APPLYING ADD MASK");
        Ok(())
    }
    fn undo(&mut self, target: &mut AppState) -> Result<(), String>{
        Ok(())
    }
    fn redo(&mut self, target: &mut AppState) -> Result<(), String> {
        self.apply(target)
    }
}

#[enum_dispatch]
pub enum AppActionTest {
    AM(AddMask)
}

fn main(){
    dbg!("running");
}

gives error statement:

error: custom attribute panicked
  --> src\main.rs:41:1
   |
41 | #[enum_dispatch]
   | ^^^^^^^^^^^^^^^^
   |
   = help: message: Unsupported argument type

error[E0412]: cannot find type `AppActionTest` in this scope
  --> src\main.rs:19:33
   |
19 |     fn merge(&mut self, _: &mut AppActionTest) -> Merged {
   |                                 ^^^^^^^^^^^^^ not found in this scope

error: aborting due to 2 previous errors

I created a repo with this code if you'd like to run it.