How to handle null columns while using minus

[ramanammurthy]

select distinct item_code ,item_description ,item_type_name,item_group_name
from tblitemmaster
minus
select distinct item_code ,item_description ,to_char(null) as item_type_name, to_char(null) as item_group_name
from tblbinlocation  
where transaction_type in('Indent','MDN')
and voucher_date 
between TO_CHAR(TO_DATE('01-03-2014', 'DD-MM-YYYY')) 
and TO_CHAR(TO_DATE('31-08-2014', 'DD-MM-YYYY'))

The above query getting wrong output,it will display all records from tblitemmaster table,if it is not use null colums ,minus getting perfect output.

Insted of the above query am using not exists

select distinct item_code ,item_description,item_type_name,item_group_name
from tblitemmaster
where not exists (select distinct item_code from tblbinlocation
where tblitemmaster.item_code = tblbinlocation.item_code 
and transaction_type in('Indent','MDN') and 
voucher_date  
between TO_CHAR(TO_DATE('01-03-2014', 'DD-MM-YYYY')) 
and TO_CHAR(TO_DATE('31-08-2014', 'DD-MM-YYYY')))

But,the above query getting correct output.

Minus and not exists concepts are same.but,the two queries are getting different output.2nd query only correct output.
How to alter the 1st query and i want correct result like 2nd query.
Thanks in advance.

[mukherjee]

You may try to use ISNULL(column, value) method.