The above default expression evaluated to be "null".
I was however able to achieve the desired result in the sql query by writing the below code to identify null in multi-select parameter:
--The Where condition will check if the Multi-Select Parameter isNull
Select 1 Data from Dual
where $X{IN, 0, param_prj_id}
UNION ALL
--The Where condition will check if the Multi-Select Parameter isNotNull
Select 2 Data from Dual
where $X{NOTIN, 0, param_prj_id}
If I get Null in Multi-Select I simply set the data variable to 1(lets say - test) and use this 'test' variable on a band as display expression. when $F{test} == 1.
The actual query is much more complicated, but this exactly what i needed :)
