Datatables Object Reference not set to instance of an object for one variable - asp.net

Question

This is my datatables serverside implementation. FilterInput contains 5 variables:
Level <- string
Message <- string
Exception <-string
StartDate <- DateTime
EndDate <- DateTime
For some reason when I run this code as it is, I will always get this error:
{System.NullReferenceException: Object reference not set to an
instance of an object.
This is referring to this line:
data = data.Where(
u => u.Level.ToString().ToLower().Contains(FilterInput.Level.ToLower()) &&
u.Message.ToString().ToLower().Contains(FilterInput.Message.ToLower()) &&
u.Exception.ToString().ToLower().Contains(FilterInput.Exception.ToLower())
).ToList();
However, if I remove the search for FilterInput.Exception, everything runs fine again. I have tested it with input ("abc") or without input ("") and the results are the same. The other FilterInputs don't have the same error.
public JsonResult Search(SearchViewModels Input, EventLogsSearchViewModel FilterInput)
{
JsonResult result = new JsonResult(null);
try
{
var data = dbContext.EventLogs.ToList();
int totalRecords = data.Count;
var modelStructure = new Dictionary<int, string>();
modelStructure.Add(1, "Level");
modelStructure.Add(2, "TimeStamp");
modelStructure.Add(3, "LogEvent");
modelStructure.Add(4, "Message");
modelStructure.Add(5, "MessageTemplate");
modelStructure.Add(6, "Exception");
modelStructure.Add(7, "Properties");
var StartDate = FilterInput.StartDate != default(DateTime);
var EndDate = FilterInput.EndDate != default(DateTime);
if ((!string.IsNullOrEmpty(FilterInput.Level) && !string.IsNullOrWhiteSpace(FilterInput.Level)) ||
(!string.IsNullOrEmpty(FilterInput.Message) && !string.IsNullOrWhiteSpace(FilterInput.Message)) ||
(!string.IsNullOrEmpty(FilterInput.Exception) && !string.IsNullOrWhiteSpace(FilterInput.Exception)) ||
(StartDate && EndDate))
{
data = data.Where(
u => u.Level.ToString().ToLower().Contains(FilterInput.Level.ToLower()) &&
u.Message.ToString().ToLower().Contains(FilterInput.Message.ToLower()) &&
u.Exception.ToString().ToLower().Contains(FilterInput.Exception.ToLower())
).ToList();
data = data.Where(u => u.TimeStamp >= FilterInput.StartDate && u.TimeStamp <= FilterInput.EndDate).ToList();
}
if (!(string.IsNullOrEmpty(Input.Order) && string.IsNullOrEmpty(Input.OrderDir)))
{
var columnName = modelStructure.FirstOrDefault(f => f.Key == Convert.ToInt32(Input.Order));
data = data.AsQueryable().OrderBy(columnName.Value + " " + Input.OrderDir).ToList();
}
int recFilter = data.Count;
data = data.Skip(Input.StartRec).Take(Input.PageSize).ToList();
var modifiedData = data.Select(u => new EventLogsListViewModel
{
Id = u.Id,
Message = u.Message,
MessageTemplate = u.MessageTemplate,
Level = u.Level,
TimeStamp = u.TimeStamp,
Exception = u.Exception,
Properties = u.Properties,
LogEvent = u.LogEvent
});
result = this.Json(new
{
draw = Convert.ToInt32(Input.Draw),
recordsTotal = totalRecords,
recordsFiltered = recFilter,
data = modifiedData,
order = Input.Order,
orderdir = Input.OrderDir
});
}
catch (Exception e)
{
logger.LogError(e, LoggingGlobals.LoadingException);
}
return result;
}
EDIT: The exception still happens even when FilterInput.Exception is not null