Question: I am finding difficulties in validating the following 

```
if(personDS.person[0].IdFk!= DBNull.Value)

```

this is the compile time error - cannot be applied to operands of type 'System.Guid and 'System.Dbnull'

Answer: 
I think you should check:

```
if(personDS.person[0].IsIdFkNull())

```
Id is a Guid, which is a Value type and will therefore never equal DBNull.Value. Before I can fully help, I will need to know the types of `personDS` (DataSet maybe?) and `person` (DataTable maybe). Assuming so, then maybe:

```
if (!personDS.person[0].IsNull("IdFK"))

```

If `person` is not a DataTable but a class then check for either `IdFk == Guid.Empty`, if `IdFk` is a Guid, or `IdFk == null` if `IdFk` is `Guid?`.