constructor(filePath: string = null) {
   let config;
   if (filePath) {
     config = dotenv.parse(fs.readFileSync(filePath));
   } else {
     config = dotenv.config().parsed;
   }
   this.envConfig = this.validateInput(config);
 }

async function loadEnv(envFile: string) {
  const data = await orNullIfFileNotExist(readFile(envFile, "utf8"))
  if (data == null) {
    return null
  }

  const parsed = parseEnv(data)
  for (const key of Object.keys(parsed)) {
    if (!process.env.hasOwnProperty(key)) {
      process.env[key] = parsed[key]
    }
  }
  require("dotenv-expand")(parsed)
  return parsed
}

 constructor(filePath: string) {
   this.envConfig = dotenv.parse(fs.readFileSync(filePath));
 }