Extracting empty text fields

Hi,
I somehow solved the problem of retrieving the last record (field by field) and inserting the data in the new one. In doing I have a problem when the field copied is empty. Here is the code I'm using:

m_instruction = "Select [Master database].Polarization AS Tmp FROM [Master database] WHERE [Master database].ID = " & ID_n 'here ID_n is the last record ID
sql = m_instruction
rs.Open sql, CurrentProject.Connection
Extract = rs![tmp]
[Polarization].SetFocus
[Polarization].Text = Extract
rs.Close

If rs![tmp] is empty the code crashes...
Does anyone have a fast suggestion for taking and writing empty fields?
Thanks for your time!

bye,
Helder

PS: sorry, but I'm really starting with this Access/VB things... argh... too many things !

Sorry sorry....
I solved inserting:

If IsNull(rs![tmp]) Then
Extract = ""
Else
Extract = rs![tmp]
End If


instead of just Extract = rs![tmp]

Thanks anyway!
Bye!
helder