code: func (v *Validator) Require(field string) *ValidationResult {
  	if strings.TrimSpace(v.data.Get(field)) == "" {
  		return v.addRequiredError(field)
  	} else {
  		return validationOk
  	}
  }
docs: // Require will add an error to the Validator if data.Values[field]
  // does not exist, is an empty string, or consists of only
  // whitespace.