How to match blank field value in MS Access Database Query WHERE Clause

in my asp.net+vb code and access database there is a table named persdata where there is afield named outdetails.

i used the following query 

qstr18 = "select count(*) from PersData where  coy='tata motors'and OutDetails like ' '"

but it returens with 0 (zero) result but the data must be 2 as per my databse what is worng with this code

when i remove OutDetails like ' ' the code returns correct value but it is essential to ensure that the OutDetails is blank