IS NULL function for calculated columns

Hi Folks,

My graphical CALC Views has data where some values are NULL and some are space " ".

now i would like to convert all the NULL values as SPACE.

How can i do that?

Wha ti have tried so far ?

created a calculated column with DataType = NVARCHAR and Lenght = 2

Formulae - if(isnull("TEST"),0,1)

This works as it returns 0 for Null values and the one that are not Null is 1.

However when i try to do this -if(isnull("TEST")," ","TEST")

it throws errors-

"COLUMN store error, evaluator: type error in expression evaluator" etc.)

what DATATYPE & LENGTH should i be using to make it work so that it shows SPACE when values are NULL or SPACE else show the data.