toMap method
Implementation
Map<String, dynamic> toMap() {
Map<String, dynamic> map = {
"msgType": msgType,
"content": content,
"picUrl": picUrl,
"thumbUrl": thumbUrl,
"fileUrl": fileUrl,
"fileNam": fileNam,
"fileSize": fileSize,
};
map.removeWhere((key, value) => value == null);
return map;
}