code: func ReadFromResource(client *govmomi.Client, entity *mo.ManagedEntity, d *schema.ResourceData) {
  	customAttrs := make(map[string]interface{})
  	if len(entity.CustomValue) > 0 {
  		for _, fv := range entity.CustomValue {
  			value := fv.(*types.CustomFieldStringValue).Value
  			if value != "" {
  				customAttrs[fmt.Sprint(fv.GetCustomFieldValue().Key)] = value
  			}
  		}
  	}
  	d.Set(ConfigKey, customAttrs)
  }
docs: // ReadFromResource reads the custom attributes from an object and saves the
  // data into the supplied ResourceData.
  //
  // TODO: Add error handling and reporting to this method.