Accessing msg.MailingListHelp breaks with Null reference exception when not present.

This code:

string fullpath = Path.Combine(SelectedFolder, filepath); var msg = new Storage.Message(fullpath); var msgmlhelp = msg.MailingListHelp;

causes a Null reference exception in my code - target .Net 4.6.2. WPF app. I came across it because, not knowing which properties I actually want out of the file (I don’t need mailinglisthelp), I wrote this to extract the data:

 public Dictionary<string, string> GetMsgFileDetails(string filepath)
    {
        Dictionary<string, string> filedetails = new Dictionary<string, string>();
        //try
        {
            string fullpath = Path.Combine(SelectedFolder, filepath);
            var msg = new Storage.Message(fullpath);
            var msgmlhelp = msg.MailingListHelp;
            foreach (var prop in msg.GetType().GetProperties())
            {
                string pname = prop.Name;

                if (prop.GetValue(msg) != null)
                {
                    object pvalue = prop.GetValue(msg);
                }
                // We only want the strings
                if (prop.GetValue(msg) != null && (prop.GetValue(msg) is string))
                {
                    filedetails.Add(prop.Name, prop.GetValue(msg).ToString());
                }

            }
            return filedetails;
        }
        //catch (Exception ex)
        //{
        //    MessageBox.Show(ex.Message, "Error trying to load file");
        //    return null;
        //}
    } (try catch disabled to aid debugging) s

It was breaking out in the test for null and I found it was MailingListHelp causing it. I didnt get any further so there could be others perhaps? Any thoughts on how to work around this ? Thanks, Brett

[bendiknesbo]

If you want to future-proof it by only populating your dictionary with the properties that are retrievable by ProperyInfo.GetValue, then you can rewrite the body of the foreach as such:

var pName = prop.Name;
try {
    var value = prop.GetValue(msg);
    if (value is string str) {
        filedetails.Add(pName, str);
    }
} catch (Exception ex) {
    Log.Error($"Property \"{pName}\" in object Storage.Message was not retrievable.", ex);
    continue;
}

[bendiknesbo]

I did a quick check on a .NET 4.6 Unittest-project, using your method as a base, and found one more problematic property: MailingListUnsubscribe.

@Sicos1977 should probably look into why those two properties are throwing NullReferenceExceptions.

If you do not need those two properties, then here is a method you can use to get all properties except two that cause problems. It is not future-proofed, so if any other properties seem to cause problems, then it will need to be modified.

private readonly List<string> _msgReaderExcludeProperties = new List<string> {
	nameof(Storage.Message.MailingListHelp),
	nameof(Storage.Message.MailingListUnsubscribe),
};
public Dictionary<string, string> GetMsgFileDetails(string filepath) {
	var filedetails = new Dictionary<string, string>();
	var fullpath = Path.Combine(SelectedFolder, filepath);
	using (var msg = new Storage.Message(fullpath)) {
		foreach (var prop in msg.GetType().GetProperties()) {
			var pName = prop.Name;
			if (_msgReaderExcludeProperties.Contains(pName)) {
				continue;
			}

			var value = prop.GetValue(msg);
			// We only want the strings
			if (value is string str) {
				filedetails.Add(pName, str);
			}
		}
	}
	return filedetails;
}