sql - Check if a parameter is null or empty in a stored procedure

Question

I know how to check if a parameter is null but i am not sure how to check if its empty ... I have these parameters and I want to check the previous parameters are empty or null and then set them like below

ALTER PROCEDURE [dbo].[GetSummary]
    @PreviousStartDate NVARCHAR(50) ,
    @PreviousEndDate NVARCHAR(50) ,
    @CurrentStartDate NVARCHAR(50) ,
    @CurrentEndDate NVARCHAR(50)
AS
  BEGIN
    IF(@PreviousStartDate IS NULL OR EMPTY)
        SET @PreviousStartdate = '01/01/2010'  for example..

I would appreciate the help.

Answer 1

I sometimes use NULLIF like so...

IF NULLIF(@PreviousStartDate, '') IS NULL

There's probably no reason it's better than the way suggested by @Oded and @bluefeet, just stylistic preference.

@danihp's method is really cool but my tired old brain wouldn't go to COALESCE when I'm thinking is null or empty :-)