messageAttachment property Null safety

NIMMessageAttachment? messageAttachment
@JsonKey(fromJson: NIMMessageAttachment._fromMap, toJson: NIMMessageAttachment._toMap), read / write

消息附件内容

Implementation

@JsonKey(
    fromJson: NIMMessageAttachment._fromMap,
    toJson: NIMMessageAttachment._toMap)
NIMMessageAttachment? messageAttachment;