Error when change the option back: This value should be of the correct primitive type

1. Use the prepopulate option, save the field settings.
2. Edit the field again and choos another option (e.g. No geocoding or Geocode from an existing field)
3. You can't save the field settings anymore, because this error related to the default value:
This value should be of the correct primitive type.
4. Same problem with the entity (e.g. node) itself, you can't save the entity anymore because of this error.
5. Without this module, the option change is no problem.