UploadTask.fromJson constructor
Creates UploadTask object from json
Implementation
UploadTask.fromJson(super.json)
: assert(
['UploadTask', 'MultiUploadTask'].contains(json['taskType']),
'The provided JSON map is not an UploadTask, '
'because key "taskType" is not "UploadTask" or "MultiUploadTask.'),
fileField = json['fileField'] ?? 'file',
mimeType = json['mimeType'] ?? 'application/octet-stream',
fields = Map<String, String>.from(json['fields'] ?? {}),
super.fromJson();