code: def find_missing_env(self):
          
          missing = []
          for e in self.env:
              if e.default_val is None and e.set_val is None:
                  if e.env_name not in os.environ:
                      missing.append(e.env_name)
  
          if missing:
              raise BadOption("Some environment variables aren't in the current environment", missing=missing)
docs: Find any missing environment variables