code: func (s *Scheme) AddDefaultingFuncs(defaultingFuncs ...interface{}) error {
  	for _, f := range defaultingFuncs {
  		err := s.converter.RegisterDefaultingFunc(f)
  		if err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // AddDefaultingFuncs adds functions to the list of default-value functions.
  // Each of the given functions is responsible for applying default values
  // when converting an instance of a versioned API object into an internal
  // API object.  These functions do not need to handle sub-objects. We deduce
  // how to call these functions from the types of their two parameters.
  //
  // s.AddDefaultingFuncs(
  //	func(obj *v1.Pod) {
  //		if obj.OptionalField == "" {
  //			obj.OptionalField = "DefaultValue"
  //		}
  //	},
  // )