columnDefs.data

I'm working on a column that is a calculated value, using the columnDef.data option. When I had the column defined like this:

{  data: null, title:"Outlier" }

my columnsDef was ignored. I had to change the column declaration to this

    {  title:"Outlier" }    ,   

to get it to work. Is that expected?

Also, is there a difference between using columnDefs.data()

columnDefs: [
        { targets: [ -6 ], data: function (row, type, val, meta) {
                    do some crazy business logic 
                       return myresult;
               }
        ]

and doing the same thing (with a function) in the columns.data option?