Should pick the same environment key as the default key if the config doesn't have any default.

[suthagar23]

{
   "APP_SECRET": {
      "DEV" : "12345"
   }
}

In the above example, the .env.config doesn't have any default mapping value. Better to have the default parse value key as the same configuration key - APP_SECRET. So finally, it should parse the following config,

{
   "APP_SECRET": {
      "DEV" : "12345",
      "DEFAULT" : "{{APP_SECRET}}"
   }
}

Here, the user will have the freedom to pass this value outside from .env.config.

APP_SECRET=123 node index.js