typeof with template literal does not narrow union #20949

interface ProcessEnv {
  [key: string]: string | undefined;
}

const env: ProcessEnv = { FOO: 'bar' };
const envVar: string | undefined = env.FOO;
if (typeof envVar === `string`) {
  // error TS2532: Object is possibly 'undefined'.
  console.log(envVar.slice(0));
}
if (typeof envVar === 'string') {
  console.log(envVar.slice(0));
}