fix dbnull error

app/BrainpoolXmlParser/DB.vb

@@ -66,6 +66,10 @@ Public Class DB
         Dim sql = String.Format("SELECT VALUE FROM {0} WHERE CONTROL_ID = {1} AND RECORD_ID = {2}", table, controlId, recordId)
         Dim value = Me.Scalar(sql)
 
+        If (IsDBNull(valueToCompare) Xor IsDBNull(value)) Then
+            Return False
+        End If
+
         Return value = valueToCompare
     End Function