Check For Null

I am trying to create a stored proc.
I have to check a parameter for null value and if null then set it to zero
Here is the stored proc
set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go
ALTER PROCEDURE [dbo].[UPDATENOA]
(
@Accepted char(10),
@NOAId bigint,
@Court char(30),
@RetainerType char(30),
@PendingInTaxCourt char(1)
)
AS
begin
UPDATE NOA set StageCode = Accepted,Court=@Court,RetainerType=@RetainerType,PendingInTaxCourt=@PendingInTaxCourt where NOAId = @NOAId;
Declare @Sequence int
Select @Sequence = MAX(Sequence) From [dbo].[NOAStages] where NOAId=@NOAId;
if @Sequence IS NULL
{
@Sequence=0
}
Insert into [dbo].[NOAStages] (NOAId,StageCode,Sequence)
values (@NOAId,@Accepted,@Sequence+1)
But this is giving me error. What is the correct way to do this.
Thanks