1900-01-01 in date field problem

I have a function that deals with NULLS a datefield.

This works to a point but puts in the date 1900-01-01  when a NULL is entered from    FW_DATECOMPLIANTTextBox.TexT

        Dim dtDateCompliant As String = FW_DATECOMPLIANTTextBox.Text
            If String.IsNullOrEmpty(dtDateCompliant) Or Not IsDate(dtDateCompliant) Then
                FW_DATECOMPLIANTTextBox.Text = ""
                dtDateCompliant = System.Data.SqlTypes.SqlDateTime.Null
                cmd.Parameters.AddWithValue("@FW_DATECOMPLIANT", dtDateCompliant)
            Else
                cmd.Parameters.AddWithValue("@FW_DATECOMPLIANT", CDate(dtDateCompliant))
            End If

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How can I solve this so it just inputs NULL?