How to make multi value parameter optional in SSRS

I HAVE REPORT IN SSRS 2005.

I have @strjournal as multi value parameter. Allow blank is checked. Parameter values r assigned through query.

select jornalno,jornalno as descr from tran_table 

union select 'NULL','NULL' 

So for @strjournal,  valuefield = jornalno  , label field = descr

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my main query i am giving,

select .... from myTable where  (TRANKEY IN (@strjournal) AND @strjournal<> 'NULL' ) OR (TRANKEY LIKE '%' AND @strjournal = 'NULL')

If i select 'NULL' its giving me correct result (returning all records as condition is like '%')

if i select only 1 journalno (not 'NULL') also giving me correct result (i.e. only 1 record for which jornalno is selected)

if i select more than 1 jornalnos then its giving me error "an expression of non boolean type specified in a context where condition is expected , near ','"

Any help ??

h2007