Custom terraform provider read data

Terraform Providers
1

HI, I tried to create my terraform provider.
With POST method looks good.

Read method return empty. However I see, flattening created proper map.
I checked example avenger and got the same issue.
Here is avenger main.tf:
cat main.tf
terraform {
required_providers {
avengers = {
version = “1.0.1”
source = “github.com/sourav977/avengers”
}
}
}

provider “avengers” {
host = “http://localhost:8000”
}

data “avengers_datasource” “all” {}

output “all_avang” {
value=data.avengers_datasource.all.avengers
}
Output is empty, however if I created resource - output is correct.
I checked aws provider, availabilty zone - return proper input.

Could you please provide example read only provider

Thanks,
Dmitriy