code: func MakeGetEnv(ctx context.Context) func(string) string {
  	return func(key string) string {
  		if v := LookupEnv(ctx, key); v.Exists {
  			return v.Value
  		}
  		return ""
  	}
  }
docs: // MakeGetEnv returns a function bound to the supplied Context that has the
  // same semantics as os.Getenv. This can be used to simplify environment
  // compatibility.