code: func SetBoolStringPtr(d *schema.ResourceData, key string, val *bool) error {
  	var s string
  	if val != nil {
  		s = strconv.FormatBool(*val)
  	}
  	return d.Set(key, s)
  }
docs: // SetBoolStringPtr sets a stringified ResoruceData bool field. This is a field
  // that is supposed to behave like a bool (true/false), but needs to be a
  // string to represent a nil state as well.
  //
  // This is designed to address the current lack of HCL and Terraform to be able
  // to distinguish between nil states and zero values properly. This is a
  // systemic issue that affects reading, writing, and diffing of these values.
  // These issues will eventually be addressed in HCL2.