toJson method
Converts this link to a data object.
Implementation
Map<String, dynamic> toJson() => {
// set required fields
'href': href,
// set optional fields if available
if (rel != null) 'rel': rel,
if (type != null) 'type': type,
if (hreflang != null) 'hreflang': hreflang,
if (title != null) 'title': title,
if (length != null) 'length': rel,
};