stored procedure in sqlserver

Question

How to check the condition 

 

this is my sp

 

how to check the id is null in the sp  

 

alter PROCEDURE Check_Exist

(

@Id INT,

@balance money

)

AS

BEGIN

If @Id is null

IF NOT EXISTS (SELECT AccountId FROM Account WHERE [AccountId]=@Id)

BEGIN

INSERT INTO Account VALUES(@Id,@balance)

PRINT 'New Record Insert Successfuly'

END

ELSE

BEGIN

PRINT 'Id All Ready Exist'

END

END

 

please help me this