How do I panic the build of a Vue 2 project if an environment variable is not set?

In a Vue 2 project, an environment variable (let it be VUE_APP_IMPORTANT_VAR, for example) is mandatory, so I want to get a failed build if somebody has forgotten to specify the variable in .env (or in another way). I tried this code:

/* main.js */
...

if (!process.env.VUE_APP_IMPORTANT_VAR) {
  console.error("Critical: VUE_APP_IMPORTANT_VAR is not set")
  throw 1
}

...

But this obviously gives successful build. So how do I break the build if the variable is not set?