If/then Parameterized Queries Using Tableadapter

Hey fellas.  Here's my situation.  I have two textboxes where the user enters a "start" date and an "end" date.  I want to search a table to find records who's "expired" column date is between those two dates provided by the user.  The tricky part is, if the user just puts a start date in but no end date, I want it to search from whatever start date the user entered to the future and beyond.  Essentially, I think I'm looking for a SQL statement along the lines of:

  SELECT Request.RequestID, Request.URL, ActionProvider.Name, Request.CurrentStageID, Request.Decision, Request.SubmissionDate,
Request.ExpirationDate
FROM Request INNER JOIN
RequestSpecificActionProvider ON Request.RequestID = RequestSpecificActionProvider.RequestID INNER JOIN
ActionProvider ON RequestSpecificActionProvider.ActionProviderID = ActionProvider.ActionProviderID INNER JOIN
RoleActionProvider ON ActionProvider.ActionProviderID = RoleActionProvider.ActionProviderID INNER JOIN
Role ON RoleActionProvider.RoleID = Role.RoleID
WHERE

CASE WHEN @BeginDate is not null AND @BeginDate <> ''
THEN Request.ExpirationDate > @BeginDate
END

AND

CASE WHEN @EndDate is not null AND @EndDate <> ''
THEN Request.ExpirationDate > @EndDate
END

AND (Role.Description = 'Requestor')


 

I realize my code isn't correct and there's still a floating "AND" out there I would have to put some logic around.  Anyway, how do I do this?  Do I need to build three separate queries in my tableadapter (one for if both dates are provided, one for if start date is provided, one for if end date is provided) and build the logic in my application code or can I tackle it with SQL?  If I can tackle it with SQL, where have I gone astray?  I'm currently getting the error: "Error in WHERE clause near '>'. Unable to parse query text."

 Thanks for the help everyone!