code: func (mr *modelRef) elemValue() reflect.Value {
  	if mr.value().IsNil() {
  		msg := fmt.Sprintf("zoom: panic in elemValue(). Model of type %T was nil", mr.model)
  		panic(msg)
  	}
  	return mr.value().Elem()
  }
docs: // elemValue dereferences the model and returns the
  // underlying struct. If the model is a nil pointer,
  // it will panic if the model is a nil pointer