code: func (converter MarkupConverter) Convert(value interface{}, item AttributeAccessor) (interface{}, error) {
  	// return a 'nil' result if the supplied 'value' was nil
  	if value == nil {
  		return nil, nil
  	}
  	switch value.(type) {
  	case string:
  		return rendering.NewMarkupContent(value.(string), converter.markup), nil
  	default:
  		return nil, errors.Errorf("Unexpected type of value to convert: %T", value)
  	}
  }
docs: // Convert returns the given `value` if the `item` is not nil`, otherwise returns `nil`