I have a start and end date in my application. If a user does not know their
dates yet, I want them, they will be null in the DB and I want them to be
blank in the application. So, I'm trying to figure out how to use a nullable
date, and want to return it in my method.

I tried to cast the output parameter, but I get a run-time cast error:
return new TimeLine((DateTime?)command.Parameters["@startDate"].Value,
(DateTime?)command.Parameters["@endDate"].Value);

Then I changed to the code to what you see below, and it worked. But I am
wondering is there a better way to do this when working with nullable dates?

DateTime? startDate;
DateTime? endDate;

if (command.Parameters["@startDate"].Value is DBNull)
    startDate = null;
else
    startDate = (DateTime?)command.Parameters["@startDate"].Value;

if (command.Parameters["@endDate"].Value is DBNull)
    endDate = null;
else
    endDate = (DateTime?)command.Parameters["@endDate"].Value;

return new TimeLine(startDate, endDate);