vb.net - LINQ error type DBNull column -

i querying datagridview , works great unless 1 of cells has nothing (dbnull). how on come this?

exceptions: operator '=' not defined type 'dbnull' , type 'dbnull'.

dim query = row datagridviewrow in datagridview1.rows _             row.cells(selectedcolumnindex).value = filter _             , row.visible = false _             select row distinct 

use .equals() method compare values in 1 may null. example:

dim query = row datagridviewrow in datagridview1.rows _         row.cells(selectedcolumnindex).value.equals(filter) _         , !(row.visible) _         select row distinct 

or if both may null, can use base object.equals() method compare:

dim query = row datagridviewrow in datagridview1.rows _             object.equals(row.cells(selectedcolumnindex).value, filter) _             , !(row.visible) _             select row distinct