diff --git a/modules/purchase_trade/payment_term.py b/modules/purchase_trade/payment_term.py
index 846b870..95320bd 100755
--- a/modules/purchase_trade/payment_term.py
+++ b/modules/purchase_trade/payment_term.py
@@ -36,6 +36,7 @@ class PaymentTermLine(metaclass=PoolMeta):
 
     eom_flag = fields.Boolean('EOM Flag')
     eom_mode = fields.Selection([
+        (None, ''),
         ('standard', 'Standard'),
         ('before', 'Before EOM'),
         ('after', 'After EOM'),