Dotenv no custom-config

Olá,

Eu gostaria de saber se é possível usar o pacote dotenv no custom-config do express. Se sim como isso seria possível? Eu tentei da seguinte forma:

var dotenv = require('dotenv');

app.use(dotenv.config());

Mas acabo recebendo esse erro:

 throw new TypeError('app.use() requires a middleware function')
    ^

TypeError: app.use() requires a middleware function
    at Function.use (C:\Users\ArthurGrigolettoNava\Documents\Projects\communication-hub\server\node_modules\express\lib\application.js:210:11)
    at module.exports (C:\Users\ArthurGrigolettoNava\Documents\Projects\communication-hub\server\config\custom-express.js:14:9)
    at Object.<anonymous> (C:\Users\ArthurGrigolettoNava\Documents\Projects\communication-hub\server\server.js:1:107)
    at Module._compile (internal/modules/cjs/loader.js:702:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
    at Module.load (internal/modules/cjs/loader.js:612:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
    at Function.Module._load (internal/modules/cjs/loader.js:543:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:744:10)
    at startup (internal/bootstrap/node.js:240:19)