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())

```
try 

```
if(!(personDS.person[0].IdFk is System.DBNull))

```