toJson method
Implementation
toJson() {
final Map<String, dynamic> j = {'type': type};
if (id != null) j['id'] = id;
if (attributes != null) j['attributes'] = attributes;
if (meta != null) j['meta'] = meta;
if (self != null) j['links'] = {'self': self};
if (_relationships.isNotEmpty) j['relationships'] = _relationships;
return j;
}