How do I get pending, certified value and both values from SQL server 2008

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SQL-Server

Hi,
here i have demo in which i have to calculate pending activity,certified activity and All(Pending+Certified).Problem is that i have used

NULL => FOR PENDING
NOT NULL=> FOR CERTIFIED AND
"" => FOR ALL(PENDING + CERTIFIED).

these value comes from c# coding as parameter to stored procedure.

What I have tried:

Following is my stored procedure

create  Procedure [dbo].[PROC_DPRREGISTER1_1] @PACKAGEDESCR VARCHAR(50),@VOUCHERFROMDT VARCHAR(20),@VOUCHERTODT VARCHAR(20),@STATUS VARCHAR(10),@RefNo varchar(10),@CONTRACTOR varchar(50)
AS
begin

--Declare @qry;
--set @qry=
select  * from DPRReg_R2 where PACKAGEDESCR=@PACKAGEDESCR  AND VOUCHERDT between @VOUCHERFROMDT AND @VOUCHERTODT
AND 
SUBACTIVITY = Case when len(@RefNo) >0 then @RefNo else SUBACTIVITY End 
And 
isnull(WDNO,'NULL') = case when @STATUS='NULL' THEN  'NULL'  
            WHEN @STATUS='NOT NULL' THEN  WDNO
            ELSE WDNO
       END
        AND Contractor=
        Case when  LEN(@CONTRACTOR)>0 then @CONTRACTOR else Contractor
        end 
end

1. This query is for NULL VALUES i.e for Pending

EXEC [PROC_DPRREGISTER1_1] 'RML ACADEMY-LUCKNOW' ,'2017-04-01','2017-04-20','NULL','',''

2. This query is for NOT NULL VALUES i.e for CERTIFIED
<pre>EXEC [PROC_DPRREGISTER1_1] 'RML ACADEMY-LUCKNOW' ,'2017-04-01','2017-04-20','NOT NULL','',''

3. This query is for ALL VALUES i.e for CERTIFIED+PENDING

EXEC [PROC_DPRREGISTER1_1] 'RML ACADEMY-LUCKNOW' ,'2017-04-01','2017-04-20','','',''

Its works fine for pending and certified but something wrong with All.i.e when i have pending 20 records and 115 certified 115 records then All should be 135 but my query shows 115 means it again shows certified records only
Please help me..
thanks.