Conversion from type 'DBNull' to type 'String' is not valid.

Hi all,
Please help me in this code:

txtLastNameFM.Text = IIf(dgFamilyMember.CurrentRow.Cells(3).Equals(Syst em.DBNull.Value), "", dgFamilyMember.CurrentRow.Cells(3).Value)

this is an error I get:
Conversion from type 'DBNull' to type 'String' is not valid.

I know the value of the dgFamilyMember.CurrentRow.Cells(3).Value= null but the first part of the iif returns false! What is wrong here?

I need to check the value of dgFamilyMember.CurrentRow.Cells(3).Value) to see if it is Null I need to fill txtlastname.text by "" otherwise I want to have the dgFamilyMember.CurrentRow.Cells(3).Value in that textbox.
Please help me.

re: Conversion from type 'DBNull' to type 'String' is not valid.

You can't compare strings to DBNulls like that.

re: Conversion from type 'DBNull' to type 'String' is not valid.

I need to check the value of dgFamilyMember.CurrentRow.Cells(3).Value) to see if it is Null I need to fill txtlastname.text by "" otherwise I want to have the dgFamilyMember.CurrentRow.Cells(3).Value in that textbox.

Please help me.

re: Conversion from type 'DBNull' to type 'String' is not valid.

I found it.
I used IsDBNull(expression) before assigning to a string.