How to add nestjs-asyncapi annotations to method without payload?

I'm building an API documentation using nestjs-asyncapi. Currently the API is properly generated for the endpoints containing a body (DTO) and properly annotated. However, if I add an @AsyncApiSub annotation for a methods that don't have a body (with payload: null) I get the error:

.../node_modules/@nestjs/swagger/dist/services/schema-object-factory.js:73
        const { prototype } = type;
                ^
TypeError: Cannot destructure property 'prototype' of 'type' as it is null.

Here is an example of the code that generates such an error:

...
import { AsyncApiSub } from 'nestjs-asyncapi';

@WebSocketGateway()
export class ActivityGateway {
    constructor(
        private activityService: ActivityService,
    ) {}
    @SubscribeMessage(ActivityActions.ADD_ACTIVITY)
    @AsyncApiSub({
        channel: ActivityActions.ADD_ACTIVITY,
        message: {
            payload: CreateActivityTemplateDto,
        },
    })
    public async addActivity(
        @ConnectedSocket() socket: ClientSocket,
        @MessageBody() body: CreateActivityTemplateDto,
    ): Promise<ActivitySettings> {
        return this.activityService.createNewActivityTemplate(socket.userId, body);
    }

    @SubscribeMessage(ActivityActions.GENERATE_DEMO_ACTIVITY)
    @AsyncApiSub({ channel: ActivityActions.GENERATE_DEMO_ACTIVITY, message: { payload: null } })
    public async generateDemoActivity(@ConnectedSocket() socket: ClientSocket): Promise<Activity[]> {
        return this.activityService.generateDemoActivity(socket.userId);
    }
}

How can I add the Operation ActivityActions.GENERATE_DEMO_ACTIVITY to my API documentation?

What did you try and what were you expecting?

I tried to add AsyncApiSub annotation with null payload:
@AsyncApiSub({ channel: ActivityActions.GENERATE_DEMO_ACTIVITY, message: { payload: null } }) And I also tried to add the empty annotation AsyncApiSub().
I expect to see the operation ActivityActions.GENERATE_DEMO_ACTIVITY listed in my API documentation.

Solution

To solve this problem I made the following dto:

export class EmptyDto {}

Then I add this dto to annotations of all endpoints that don't have a body. Here is one example:

@AsyncApiSub({
    channel: ActivityActions.GENERATE_DEMO_ACTIVITY,
    message: {
        payload: EmptyDto,
    },
})