code: func NestedFieldCopy(obj map[string]interface{}, fields ...string) (interface{}, bool, error) {
  	val, found, err := NestedFieldNoCopy(obj, fields...)
  	if !found || err != nil {
  		return nil, found, err
  	}
  	return runtime.DeepCopyJSONValue(val), true, nil
  }
docs: // NestedFieldCopy returns a deep copy of the value of a nested field.
  // Returns false if the value is missing.
  // No error is returned for a nil field.