Integer yes/no parameter

hello All

i have a simple table showing values below on a dataset called timesheets

name  surname          date         jobid  splitconsultant

test   test1         01/01/2013    j1000         bob

test2    test2         01/10/2014  j3456    

i have written parameter 

type integer 

yes = 1

no =0 

and what i want is the filter on the dataset to filter the names if splitconsultant is null or has a value in it. i have chosen to show all records as default but am getting a failed to evaluate filter values

i am using this code for the filter

=iif(isnothing(Fields!SplitConsultant.Value)or Fields!SplitConsultant.Value ="",Parameters!split.Value="Yes","No") and have tried

=iif(isnothing(Fields!SplitConsultant.Value)or Fields!SplitConsultant.Value ="",Parameters!split.Value="0","1") 

but not getting any further! 

any ideas! 

Steve mason