code: func (j *Job) ArgString(key string) string {
  	v, ok := j.Args[key]
  	if ok {
  		typedV, ok := v.(string)
  		if ok {
  			return typedV
  		}
  		j.argError = typecastError("string", key, v)
  	} else {
  		j.argError = missingKeyError("string", key)
  	}
  	return ""
  }
docs: // ArgString returns j.Args[key] typed to a string. If the key is missing or of the wrong type, it sets an argument error
  // on the job. This function is meant to be used in the body of a job handling function while extracting arguments,
  // followed by a single call to j.ArgError().