how do you insert a null value in a parameterized SQL statement?

[Desolator144]

Now that I've switched over to parameterized queries, everything is great except along with handling all the special characters that would otherwise disrupt an all text SQL stament, it's handling the word NULL. My code basically does this for every variable used in the entire SQL statement:

If strCallName = "" Then
      strCallName = "NULL"
End If

and for the parameter adding:

m_nonQCMD.Parameters.AddWithValue("@strCallName", strCallName)

and that worked great for my old all text ones because leaving the word NULL out of single quotes would tell it yeah, that's actually null and pass it a true null value. Now with parameterized ones, it's literally passing it the word NULL I tried just leaving the string empty but then when I try to execute the command, it says that the parameter cannot be a zero length string. So how do you give a null value to a a parameterized query and make it actually send that to the database in the statement? Would strCallName = vbNull work or would it still say it's a zero length string?