getFilter issue for blank field and field with single value

Hi there,
I am using flexmonster's slice.reportFilters to set a reportFilters
and then apply setFilter() api to set the filters. Afterwards I call getFilters() api, this gives me confirmation that filter is applied or not.
But when I applied the filter to a 'field' that has only one value then the getFilters() does not return the applied filter, it return 'null'. I know that filter is applied but getFilter() does not return the applied filter.
Now, the problem is that
case 1> if I applied a filter to a 'field' which doesn't exist(here, i am using csv data and csv doesn't have that field) then getFilter() return 'null'.
case 2> if I applied filter to a 'field' which has only one value, then getFilter() return 'null'
 

How should I distinguish it from both of then?
 
 
For example
Consider this as csv data
id name address
1    a       xyz
2    b       xyz
3    c        xyz
4    d       xyz
for case 1
flexmonster.setFilter("rollno", "rollno.[rollno1]");
flexmonster.getFilter() ==> #return null
for case 2
flexmonster.setFilter("address", "address.[addressxyz]]');
flexmonster.getFilter() ==> #return null

Flexonster version => version: "2.6.3"