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())

```
Is IdFk declared as nullable ? 
Es: 

```
public Guid? Idfk 

```

If so you can : 

```
if(personDS.person[0].IdFk.HasValue)

```