diff --git a/setra_client/models.py b/setra_client/models.py
index 7b2c25cbe89d6700b65c7fa212e61c8fe1a1ecc2..bb2d177e319d60561c052bc3937c3fae7ca307dd 100644
--- a/setra_client/models.py
+++ b/setra_client/models.py
@@ -60,11 +60,13 @@ class Voucher(BaseModel):
 
 
 class Batch(BaseModel):
-    """Model representing a batch, with a list of vouchers (and each voucher has a list of transactions)"""
+    """
+    Model representing a batch, with a list of vouchers (and each
+    voucher has a list of transactions)
+    """
     client: str
     batchid: str
-    period: str
+    period: typing.Optional[str]
     interface: str
     vouchertype: typing.Optional[str]
     vouchers: typing.List[Voucher]
-