code: func GetError(args ...interface{}) error {
  	for i := len(args) - 1; i >= 0; i-- {
  		arg := args[i]
  		if arg != nil {
  			if err, ok := arg.(error); ok {
  				return err
  			}
  		}
  	}
  	panic("no argument of type error")
  }
docs: // GetError returns the last argument that is of type error,
  // panics if none of the passed args is of type error.
  // Note that GetError(nil) will panic because nil is not of type error but interface{}