Stored Procedure Using A Parameter Default To Select ALL Records - Help Please

Hi everyone,

I have created a stored procedure in sql server with parameters for my c# application. Wanted to know is there anyway to set the default value for @searchpostcode to select all the records?

Right now it brings the records based on the postcode specified .(I have dropdownlist in my c# application that passes the parameters for postcode)

My stored procedure:

CREATE PROCEDURE sp_accepting_practice  (@searchpostcode as nvarchar(100))
  
AS

SELECT   dbo.tbdentists.Title, dbo.tbdentists.FirstName, dbo.tbdentists.Surname, dbo.tbpractices.PracticeName, dbo.tbpractices.PracticeAddress1, dbo.tbpractices.PracticeAddress2, dbo.tbpractices.Town, dbo.tbpractices.Postcode, dbo.tbpractices.Phone, dbo.tbdentistspractices.ListNo, dbo.tbtreatment.treatmentNature
FROM         dbo.tbdentists INNER JOIN dbo.tbdentistspractices ON dbo.tbdentists.DentistId = dbo.tbdentistspractices.DentistId INNER JOIN
                      dbo.tbpractices ON dbo.tbdentistspractices.PracticeId = dbo.tbpractices.PracticeId AND
                      dbo.tbdentistspractices.PracticeId = dbo.tbpractices.PracticeId INNER JOIN
                      dbo.tbtreatment ON dbo.tbdentistspractices.TreatmentId = dbo.tbtreatment.treatmentId
WHERE   dbo.tbpractices.Postcode LIKE '%' + @searchpostcode + '%'
ORDER BY dbo.tbpractices.PracticeId


EXECUTE sp_accepting_practice   G4
GO

I greatly appreciate your help. Thanks in Advance

Regards

Shini