code: func InvalidParamTypeError(name string, val interface{}, expected string) error {
  	msg := fmt.Sprintf("invalid value %#v for parameter %#v, must be a %s", val, name, expected)
  	return ErrInvalidRequest(msg, "param", name, "value", val, "expected", expected)
  }
docs: // InvalidParamTypeError is the error produced when the type of a parameter does not match the type
  // defined in the design.