code: func GetClass(err error) *ErrorClass {
  	if err == nil {
  		return nil
  	}
  	cast, ok := err.(*Error)
  	if !ok {
  		return findSystemErrorClass(err)
  	}
  	return cast.class
  }
docs: // GetClass will return the appropriate error class for the given error.
  // If the error is not nil, GetClass always returns a hierarchical error class,
  // and even attempts to determine a class for common system error types.