If you take a look at the code for AddLogTypeConfigInfo(), you'll see that there are 3 properties that are converted to strings, see lines 10, 11 and 12 below. In the sample code you posted, you are not initializing these properties and they have no default values established in the Info class, so when you pass the Info object to AddLogTypeConfigInfo(), the lines which attempt to convert the null values to strings are throwing the exception you are seeing. So just set those 3 properties in your ltci object before calling the controller add method.
1: public virtual void AddLogTypeConfigInfo(LogTypeConfigInfo logTypeConfig)
2: {
3: LoggingProvider.Instance().AddLogTypeConfigInfo(logTypeConfig.ID,
4: logTypeConfig.LoggingIsActive,
5: logTypeConfig.LogTypeKey,
6: logTypeConfig.LogTypePortalID,
7: logTypeConfig.KeepMostRecent,
8: logTypeConfig.LogFileName,
9: logTypeConfig.EmailNotificationIsActive,
10: Convert.ToString(logTypeConfig.NotificationThreshold),
11: Convert.ToString(logTypeConfig.NotificationThresholdTime),
12: Convert.ToString(logTypeConfig.NotificationThresholdTimeType),
13: logTypeConfig.MailFromAddress,
14: logTypeConfig.MailToAddress);
15: }