SELECT 
       * 
FROM 
       "tbl_Employees" 

WHERE
     ((UPPER("Last Name")    LIKE '%' || UPPER (:Var_LN) || '%' ) OR (:Var_LN  IS NULL))
 and 
     ((      "Department-ID" =                  :Var_DPT        ) OR (:Var_DPT IS NULL))