Multiple Paramaters in a single select Statement

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SQL

Hi I am using SQL Server 2008R2

i am trying to write a query with multiple parameters that i will be using on a form in my project.

paramaters

@Startdate
@EndDate
@Product
@Store

Select Statement

Select * From table1 where (date >= @startdate and Date <= @enddate)
and Product = @product and Store=@Store

the problem i am having is if one of the parameters values equate to '' or null then no data will be returned.

Please could someone help