I don't understand why the code NULL cannot be used with picturebox.picture.

VB Code:
  1. If (picPhoto.Picture = Null) Then

  2.             If (Errfirst = "") Then

  3.                 Errfirst = "Picture "

  4.             Else

  5.                 Errfirst = Errfirst & "& Picture "

  6.             End If

  7.         End If

What code should I replace the NULL